Search

The compound (Nacnac)Ni(μ-Br)2Li(THF)2 (Nacnac = (HC(CMeNC6H3(i-Pr)2)2) was reduced by reaction with K/Na alloy in toluene. The resulting product [((Nacnac)Ni)2(μ-η³:η³-C6H5Me)] (1) was characterized and is best described as a Ni(II) species in which electron transfer from Ni to toluene has occurred. This compound reacts with a variety of donors to give Ni(I) complexes. For example, compound 1 reacts with phosphines, nitriles, acetylenes, olefins, and ketones to give the paramagnetic complexes (Nacnac)Ni(PCy3) (2), (Nacnac)Ni(Ph2PCH2PPh2) (3), (Nacnac)Ni(NCPh) (4), (Nacnac)Ni(η²-PhCCPh) (5), (Nacnac)Ni(η²-Me3SiCCSiMe3)(6), (Nacnac)Ni(η²-H2CCPh2) (7), and (Nacnac)Ni(OCPh2) (8). In the related reaction of 1 with dimethylfulvene, electron transfer from metal to ligand is evidenced by the formation of the dimetallic species [((Nacnac)Ni(η³:η³-C5H4CMe2))2] (9). The crystal structures of 1−9 are reported, and the bonding and reactivity of these products are discussed.

This paper chronicles our work examining early-transition-metal systems incorporating phosphinimide ligands for use as olefin polymerization catalysts. Incorporation of these ancillary ligands affords unique deactivation pathways which are readily overcome by specific activation procedures and contrived ligand modification. In these ways, a new family of highly active olefin polymerization catalysts was successfully developed.

A variety of donor-stabilized cationic complexes of the form [Cp(NPt-Bu3)TiMe(L)][MeB(C6F5)3] and [Cp(NPt-Bu3)TiMe(L)][B(C6F5)4] (L = Py, 4-EtPy, 4-t-BuPy, NC5H4NMe2, PMe3, Pn-Bu3, PPh3, P(p-MeC6H4)3) have been prepared and characterized. Prolonged storage in CH2Cl2 solution resulted in chloride for methyl exchange to afford species of the form [CpTi(NPt-Bu3)Cl(L)][B(C6F5)4], [{CpTi(NPt-Bu3)Me}2(μ-Cl)][B(C6F5)4], and [CpTi(NPt-Bu3)(μ-Cl)]2[MeB(C6F5)3]2. The byproduct salt [(o-MeC6H4)3PCH2Cl][B(C6F5)4] was obtained from reactions employing the sterically demanding donor phosphine P(o-MeC6H4)3, suggesting transient generation of the cation [CpTi(NPt-Bu3)Cl(CH2Cl2)]⁺. Analogous reactivity was not seen in C6H5Cl, although the species [{CpTi(NPt-Bu3)Me}2(μ-Me)][B(C6F5)4] could be formed in this solvent. The isolated zwitterionic complex TiCp(NPt-Bu3)Me(μ-MeB(C6F5)3) readily performs insertion chemistry into the Ti−methyl bonds with diisopropylcarbodiimide and diphenylacetylene substrates to afford the cationic species [CpTi(NPt-Bu3)((Ni-Pr)2CMe)][MeB(C6F5)3], [TiCp(NPt-Bu3)(PhCCPh(Me))][MeB(C6F5)3], and [TiCp(NPt-Bu3)(PhCCPh(Me))(PMe3)][MeB(C6F5)3]. The implications of this chemistry are considered.

DFT calculations of the mechanism of polymerization for the series of catalyst models derived from CpTiMe2(NPR3) (R = Me, NH2, H, Cl, F) demonstrate the critical role of ion pairing in determining the overall barrier to polymerization and suggest that electron-donating substituents reduce this barrier. Based on these results, a family of precatalysts of general formula Cp‘TiX2(NP(NR2)3) (X = Cl, Me) were developed. This approach using computational methods to guide the synthetic efforts has afforded a new, readily accessible, and easily varied family of highly active ethylene polymerization catalysts based on titanium tris(amino)phosphinimide complexes.

The redox chemistry of phosphinimide-containing group IV metal complexes has been investigated. Reaction of the simple phosphinimide species CpTi(NPR3)Cl2 (R = Me 1, i-Pr 2) with Mg affords complexes formulated as [CpTiCl(μ-NPR3)]2 (R = Me 3, i-Pr 4). In contrast, CpTi(NPt-Bu3)Cl2 (5) is reduced by Mg to a putative Ti(II) species that can be intercepted by a variety of reagents including 2,3-dimethyl-1,3-butadiene, diphenylacetylene, phenylacetylene, bis(trimethylsilyl)acetylene, ethylene, and propylene to give monometallic metallacyclic complexes. In this fashion, the Ti(IV) metallacycles CpTi(NPt-Bu3)(CH2C(Me)C(Me)CH2), 6, CpTi(NPt-Bu3)(CPh)4, 7, CpTi(NPt-Bu3)(C(Ph)CHC(Ph)CH), 8, CpTi(NPt-Bu3)(η²-C2(SiMe3)2), 9, CpTi(NPt-Bu3)(CH2)4, 10, CpTi(NPt-Bu3)(CH2CHMe)2, 15, and CpTi(NPt-Bu3)(CH2)2(CPh)2, 16, were prepared. Related intramolecular formation of metallacycle complexes was achieved upon reduction of Cp‘Ti(t-Bu2(2-C6H4Ph)PN)Cl2 (Cp‘ = Cp 18, Cp* 19). The products [Cp‘Ti(NPtBu2(2-C6H4Ph)] (Cp‘ = Cp 20, Cp* 21) contained η⁶-interactions between Ti and the 2-phenyl substituent of the biphenyl unit. While Ti(II)-phosphinimide complexes have proven difficult to handle due to their reactivity, an unequivocal example of a Ti(II) species was obtained via reduction of Cp*Ti(NPt-Bu3)Cl2 (11) with Mg in the presence of CO, affording the species Cp*Ti(NPt-Bu3)(CO)2 (22). X-ray data for 4, 6, 7, 9, 10, 15, and 17−22 are reported.

The phosphinimine−amine ligand 1 reacts with MR3 (M = Al, Ga; R = Me, H) with loss of RH to form the complexes (i-Pr2C6H3N)C(Me)CHPPh2(NC6H3-i-Pr2)MMe2 (M = Al (2), Ga (3)) and (i-Pr2C6H3N)C(Me)CHPPh2(NC6H3-i-Pr2)AlH2 (4). Subsequent reactions of 2 and 3 with [Ph3C][B(C6F5)4] afforded [(i-Pr2C6H3N)C(Me)CHPPh2(NC6H3-i-Pr2)MMe][B(C6F5)4] (M = Al (5), Ga (6)), while similar reactions of 2 and 3 with B(C6F5)3 gave [(i-Pr2C6H3N)C(Me)CHPPh2(NC6H3-i-Pr2)MMe][B(C6F5)3Me] (M = Al (8), Ga (9)). The analogous reactions of 4 with [Ph3C][B(C6F5)4] and B(C6F5)3 resulted in the formation of [(i-Pr2C6H3N)C(Me)CHPPh2(NC6H3-i-Pr2)AlH][B(C6F5)4] (10) and [(i-Pr2C6H3N)C(Me)CHPPh2(NC6H3-i-Pr2)AlH][B(C6F5)3H](11), respectively. Crystallographic studies of 1, 2, 4, and [(i-Pr2C6H3N)C(Me)CHPPh2(NC6H3-i-Pr2)AlMe(OEt2)][B(C6F5)4] (7) are reported.

Synthetic routes to the species CpZr(NPt-Bu3)2Cl, 7, Cp2Zr(NPt-Bu3)Cl, 8, CpZr(NPt-Bu3)2Me, 9, Cp2Zr(NPt-Bu3)Me, 10, and CpZr(NPt-Bu3)2Bn, 11, were developed in a manner similar to that previously reported for zirconium phosphinimide complexes. Rather than employing metathesis routes, transamination was considered to synthesize bis-phosphinimide zirconium complexes. At ambient temperature, Zr(NPt-Bu3)3(NMe2), 15, was isolated in less than 5% yield, but could be obtained cleanly via reaction of Zr(NPt-Bu3)3Cl, 14, with LiNMe2. However, thermolysis of Zr(NEt2)4 with HNPt-Bu3 afforded Zr(NPt-Bu3)2(NEt2)2, 12, which was subsequently converted to Zr(NPt-Bu3)2Cl2, 13, upon reaction with trimethylsilyl chloride. Cationic products were generated from the reaction of Lewis acids in the presence of a donor to provide the salts [CpZr(NPt-Bu3)Me(THF)][MeB(C6F5)3], 16, [Cp*Zr(NPt-Bu3)((i-PrN)2CMe)][MeB(C6F5)3], 17, and [CpZr(NPt-Bu3)((i-PrN)2CMe)][MeB(C6F5)3], 18. Similarly, reaction of [HNMe2Ph][B(C6F5)4] with 4 generated the salt [CpZr(NPt-Bu3)Me(NMe2Ph)][B(C6F5)4], 19, while reaction of 11 with B(C6F5)3 gave the base-free product [CpZr(NPt-Bu3)2][BnB(C6F5)3], 20. Structural considerations and preliminary MO calculations support the reactivity studies that augur well for olefin polymerization activity. Experimentally, previously reported screening using MAO as a solvent scrubber/activator with 1−4 showed only moderate polymerization activities. However, use of 20 equiv of Al(i-Bu)3 as scavenger and 2 equiv of B(C6F5)3 as cocatalyst resulted in a significant increase in activity relative to that observed upon activation with MAO. Use of [Ph3C][B(C6F5)4] as the cocatalyst led to even higher ethylene polymerization activities.

The phosphinimines Ph3PNR (R = Ph 1, 2,6-Me2C6H3 2, 3,5-Me2C6H3 3, 2,6-i-Pr2C6H3 4) were prepared and used to generate the species of the form [Li(o-C6H4PPh2NR)]2·Et2O (R = Ph 5, 2,6-Me2C6H3 6, 3,5-Me2C6H3 7, 2,6-i-Pr2C6H3 8). Subsequent reactions with [Rh(μ-Cl)(COD)]2 gave the complexes Rh(COD)(o-C6H4PPh2NR) (R = Ph 9, 2,6-Me2C6H3 10, 3,5-Me2C6H3 11, 2,6-i-Pr2C6H3 12). Similarly, the Ir analogue of 9 (13) was prepared using [Ir(μ-Cl)(COD)]2. The reaction of 9 with (CH2PPh2)2 afforded Rh(PPh2CH2CH2PPh2)(o-C6H4PPh2NPh) (14). Compound 9 was also shown to react with CH2Cl2 to give two products, one of which was confirmed to be [Rh(o-C6H4PPh2NPh)(CH2-o-C6H4PPh2NPh)(μ-Cl)2Rh(COD)] (15). Similar treatment of 10 and 12 with CH2Cl2 showed no reaction, while reaction of 11 with CH2Cl2 gave a mixture of unidentified products. The related imidazole-phosphinimine ligands (N2C3H3)PPh2NR (R = Ph 18, 2,6-Me2C6H3 19) were also prepared. These ligands react with NaH to give the corresponding Na-imidazolate-phosphinimines, 20 and 21, and subsequent reaction with [Rh(μ-Cl)(COD)]2 gave the complexes Rh(COD)((N2C3H2)PPh2NR) (R = Ph 22, 2,6-Me2C6H3 23). The compounds 22 and 23 do not react with CH2Cl2. The effects of steric and electronic modifications to the ligands on oxidative addition of C−Cl bonds are discussed. DFT calculations were performed on the model fragments [Rh((C6H4)PH2NH)] and [Rh((N2C3H2)PH2NH)], and the calculated atomic charges provide some insight into the reactivity of these compounds.

The series of 2-substituted diphenylphosphine pyridines 1−5 were synthesized and subsequently oxidized with silyl or aryl azides to give the series of pyridine−phosphinimine ligands 2-(Me3SiNPPh2)C5H4N (9), 2-(2,6-Me2C6H3NPPh2)C5H4N (10), 2-(2,6-i-Pr2C6H3NPPh2)C5H4N (11), 2-(2,6-Me2C6H3NPPh2)-6-MeC5H4N (12), 2-(2,6-i-Pr2C6H3NPPh2)-6-MeC5H4N (13), 2-(2,6-Me2C6H3NPPh2)-6-BnC5H4N (14), 2-(2,6-i-Pr2C6H3NPPh2)-6-BnC5H4N (15), 2-(2,6-Me2C6H3NPPh2)-6-SiMe3C5H4N (16), 2-(2,6-i-Pr2C6H3NPPh2)-6-SiMe3C5H4N (17), 2-(2,6-Me2C6H3NPPh2)-6-PhC5H4N (18), and 2-(2,6-i-Pr2C6H3NPPh2)-6-PhC5H4N (19). Attempts to oxidize the fluorinated phosphine 2-P(C6F5)2-6-PhC5H3N (6) were unsuccessful. The ligand 9 reacted with PdCl2(PhCN)2 to the give the square-planar, diamagnetic compound (L)PdCl2 (20; L = 9), while the remaining ligands were used to prepare (L)NiBr2 and (L)FeCl2 complexes 21−30 and 31−40 (L = 10-19), respectively. In these complexes the P atoms become part of the chelate backbone. In addition, the pyridine−phosphinimines 2-(Ph3P&dbd;NCH2)(C5H4N) (44), 2-(Ph3PNCH2)-6-Me(C5H3N) (45), and 2-(Ph3PNCH2)-6-Ph(C5H3N) (46) were also prepared from the reaction of 2-azidomethyl−pyridines with PPh3. In a similar fashion the complexes (L)PdCl2 (47, 48; L = 44, 45), (L)NiBr2 (49−51; L = 44−46), (L)FeCl2 (52, 53), and (L)CoCl2 (54, 55; L = 44, 45) were prepared. In addition, the imidazole−phosphines 1-Me-2-(PPh2)C3H2N2 (58), 1-Me-2-(PPh2)-4,5-Ph2C3N2 (59), and 1-Me-2-(PPh2)C7H6N2 (60) were prepared and oxidized to give the imidazole−phosphinimines 1-Me-2-(2,6-Me2C6H3N&dbd;PPh2)C3H2N2 (61), 1-Me-2-(2,6-i-Pr2C6H3N&dbd;PPh2)C3H2N2 (62), 1-Me-2-(2,6-Me2C6H3N&dbd;PPh2)-4,5-Ph2C3N2 (63), 1-Me-2-(2,6-i-Pr2C6H3N&dbd;PPh2)-4,5-Ph2C3N2 (64), 1-Me-2-(2,6-Me2C6H3N&dbd;PPh2)C7H6N2 (65), 1-Me-2-(2,6-i-Pr2C6H3N&dbd;PPh2)C7H6N2 (66) and 1-Me-2-(2,6-i-Pr2C6H3N&dbd;PPh2)-4-(t-Bu)C3HN2 (67). Subsequent complexation afforded the species (L)PdCl2 (68; L = 61), (L)NiBr2 (69−75; L = 61−67), and (L)FeCl2 (76−82; L = 61−67). Preliminary screening for activity as catalyst precursors for ethylene polymerization indicated that ethylene oligomerization may be occurring. In the case of complexes 30, 40, 74, and 82 activation with Et2AlCl(ClC6H5) at 35 °C under 300 psi of ethylene effected modest catalytic dimerization of ethylene to mainly C4 alkenes. DFT computations suggested that inclusion of P into the ligand results in diminished electrophilicity at the metal and thus a weakened ethylene−metal interaction, accounting for the modest catalytic activity. X-ray structure determinations were obtained for 2, 20, 26, 27, 35, 37, 40, 49−51, 54, 68, 79, and 82.

The species [(Cp*Cr)2(μ-Cl)3]X (X = [AlCl4] (3), [GaCl4] (4), [B(C6F5)4] (5)) were generated from (Cp*CrCl(μ-Cl))2 (1) via reaction with a chloride abstraction reagent. Using a similar synthetic route, the reaction of 1, generated in situ, with MeLi and the borane B(C6F5)3 gave crystals of the salt [(Cp*Cr)2(μ-Cl)3][MeB(C6F5)3] (6), while the complex [(Cp*Cr)2(μ-Cl)3][Me2B(C6F5)2] (7) was obtained, albeit in low yield, from the reaction of [Cp*CrMe(μ-Cl)]2 with HB(C6F5)2. Monoalkylation of 5 with MeLi gave [(Cp*Cr(μ-Cl))2(μ-Me)][B(C6F5)4] (8), while the related mono(phosphide)-bridged cationic species [(Cp*Cr)2(μ-PPh2)(μ-Cl)2][B(C6F5)4] (9) was derived from 5 via reaction with Ph2PLi. The bis(phosphide)-bridged species [(Cp*Cr(μ-PPh2))2(μ-Cl)][AlMe3Cl] (10) was derived from reaction mixtures of 1, Ph2PLi, and AlMe3, while monoalkylation of 1 with MeLi followed by treatment with Ph2PLi and AlMe3 yielded [(Cp*Cr(μ-PPh2))2(μ-Me)][(Me3Al)2(μ-Cl)] (11). The neutral phosphide-bridged species (Cp*Cr(μ-PPh2))2(μ-CH2) (12) and (Cp*Cr)2(μ-PPh2)(μ-Cl)(μ-CH2) (13) were obtained from reactions of 1, MeLi, and Ph2PLi. X-ray structural data are reported from compounds 5−13. The synthetic routes and the structural data are discussed.

A strategy for polymerization catalyst design has been developed based on the steric and electronic analogy of bulky phosphinimides to cyclopentadienyl ligands. To this end, the family of complexes of the form (Cp^†)TiCl2(NPR3) has been prepared and characterized. Alkyl and aryl derivatives of these species have also been synthesized, and a number have been evaluated for use as catalyst precursors in olefin polymerization. The polymerization of ethylene has been examined employing several types of cocatalyst activators. Trends and patterns in the structure−activity relationship are discussed, and the implications for catalyst design are evaluated.

The preparation of a silyl−phosphinimide of the form (R3PN)SiMe3 (R = Me (1), i-Pr (2), Ph (3), t-Bu (4)) was achieved by the conventional literature methodology of oxidation of phosphine by N3SiMe3. The analogous species (t-Bu3PN)MMe3 (M = Ge (5), Sn (6)) were derived via a stoichiometric reaction of the salt Li[NP-t-Bu3] with Me3MCl. Similarly, the species (t-Bu3PN)2MMe2 (M = Si (7), Ge (8), Sn (9)), (i-Pr3PN)SnMe3 (10), (i-Pr3PN)2SnMe2 (11), and (t-Bu3PN)2SnMeCl (12) were prepared. Subsequent reactions of 12 afforded (t-Bu3PN)3SnMe (13) and (t-Bu3PN)2Sn(Ot-Bu)Me (14). In analogous metathesis reactions R3PNSnPh3 (R = t-Bu (15), i-Pr (16)), (t-Bu3PN)2SnPh2 (17), and (t-Bu3PN)2Sn(t-Bu)2 (18) were also prepared. Reaction of i-Pr3PNH and ClSnMe3 gave (i-Pr3PNH)SnMe3Cl (19), whereas 6 was obtained from the reaction of t-Bu3PNH with Me3SnCl. The reaction of 1 with B(C6F5)3 resulted in the formation of Me3PN(SiMe3)B(C6F5)3 (20), whereas the phosphinimines 2 and 3 react with B(C6F5)3 in a 2:1 ratio to give [R3PNSiMe2(N(PR3)SiMe3)][MeB(C6F5)3] (R = i-Pr (21), Ph (22)). In contrast, reaction of 4 and 6 with B(C6F5)3 afforded [((μ-t-Bu3PN)MMe2)2][MeB(C6F5)3]2 (M = Si (23), Sn (24)). The analogous reaction of 7 and 9 with B(C6F5)3 gave products formulated as [((t-Bu3PN)2MMe)2][MeB(C6F5)3]2 (M = Si (25), Sn (26)) and [((i-Pr3PN)2SnMe)2][MeB(C6F5)3]2 (27). Complexes 7−9, 17, 19, 20, and 24 were characterized crystallographically. The implications of this chemistry with regard to the steric demands of phosphinimide ligands are considered.

Mg complexes of bis(phosphoranimine)methane and -methanide ligands have been characterized. Reaction of CH2(Ph2PNSiMe3)2 with MeMgI and MeMgCl gave the crystalline products CH2(Ph2PNSiMe3)2MgI2 (1) and [HC(Ph2PNSiMe3)2Mg(μ-Cl)]2 (2), respectively. The related reaction of LiCH(Ph2PNSiMe3)2 with MeMgI afforded CH(Ph2PNSiMe3)2MgI(THF) (3). Crystallographic data for 1−3 confirm a significant Mg−C interaction in complexes containing bis(phosphoranimine)methanide ligands.

A series of titanium−phosphinimide thiolate complexes were prepared employing either thiolate for chloride metathesis or protonolysis of metal−carbon bonds by thiols. In these ways the following species were obtained:  CpTi(NPR‘3)(SR)2 (R‘ = i-Pr, R = CH2Ph 3; Ph 4, t-Bu 5, (SR)2 = S2(CH2)2 6, S2(CH2)3 7, S2(CH2)2C6H4 8; R‘ = t-Bu, R = CH2Ph 9; Ph 10, t-Bu 11); Cp(t-Bu3PN)TiMe(SPh) 12; and (t-Bu3PN)2Ti(SR)2 (R = CH2Ph 14; Ph 15, t-Bu 16). Reactions of (t-Bu3PN)2TiMe2 with 1 equiv of HSCH2Ph gave a cyclometalated species 17, (t-Bu3PN)2Ti(η²-SCHPh). The analogous reaction of 1 equiv of phenylthiol generated the species (t-Bu3PN)2Ti(Me)(SPh) 18. While 17 and 18 could not be isolated free of 14 and 15, respectively, the analogous reaction of tert-butylthiol afforded (t-Bu3PN)2Ti(Me)(St-Bu) 19 cleanly. Attempts to effect sulfur insertion into Ti−Me bonds were undertaken via the reaction of (t-Bu3PN)2TiMe2 with S8 but gave instead the species (t-Bu3PN)2Ti(η²-S5) 20. The reactivity of the thiolate derivatives, 3−5 with excess AlMe3, was examined. Spectroscopic and crystallographic studies revealed the formation of (CpTi(μ-SR)(μ-NPi-Pr3)(C)(AlMe2)2(μ-SR)AlMe (R = CH2Ph 21, Ph 22, t-Bu 23). Analogous reactions of 7 and 8 with AlMe3 afforded [Cp(i-Pr3PN)Ti(SRS)]·(AlMe3)3 (R = (CH2)3 24, ((CH2)2(C6H4)) 25). The mechanistic implications of the observed multiple C−H bond activation are considered. Crystallographic studies of 4, 6, 7, 14, 16, and 20−23 are reported.

Reaction of Li[NPt-Bu3] with FeCl2 affords [Cl3Fe2(μ-NPt-Bu3)2] 1 in 71% yield. This mixed valent Fe(III)−Fe(II) undergoes reversibly one-electron oxidation to generate [Cl3Fe2(μ-NPt-Bu3)2]⁺. Chemical oxidation with [Cp2Fe]PF6 yields [Cl2Fe(μ-NPt-Bu3)]2 2. The reaction of Li[NPt-Bu3] with FeBr3 affords [Br4Fe2(μ-NPt-Bu3)2] 3, while the reaction of FeCl3 with Me3SiNPCy3 gives [Cl2Fe(μ-NPCy3)]2 4. Hydrolysis of 3 yields the species [(t-Bu3PNH)Br2Fe]2(μ-O) 5. These species have also been evaluated as catalysts for the polymerization of ethylene and copolymerization of ethylene/octene. These species were found to be single-site catalysts even under rather demanding conditions (50−160 °C, 100−300 psig ethylene), although the activities are generally low. Compound 5 affords polymer similar to that produced by 3, suggesting that MAO dehydrates 5 generating a catalyst similar to that derived from 3. Compounds 1, 2, 4, and 5 have been crystallographically characterized.

Zirconium phosphinimide complexes of the form CpZr(NP-t-Bu3)Cl2 (1) and Cp*Zr(NPR3)Cl2 (R = i-Pr (2), t-Bu (3)) were readily prepared under ambient conditions via the reaction of [CpZrCl3]n or Cp*ZrCl3 with the appropriate trialkylphosphinimide lithium salt (R3PNLi). A series of derivatives were readily obtained via alkylation or arylation of the above dihalide precursors. These included CpZr(NP-t-Bu3)Me2 (4), Cp*Zr(NPR3)Me2 (R = i-Pr (5), t-Bu (6)), CpZr(NP-t-Bu3)Ph2 (7), Cp*Zr(NPR3)Ph2 (R = i-Pr (8), t-Bu (9)), CpZr(NP-t-Bu3)Bn2 (10), CpZr(NP-t-Bu3)(CH2SiMe3)2 (11), Cp*Zr(NPR3)(allyl)2 (R = i-Pr (12), t-Bu (13)), Cp*Zr(NPR3)(Cp)Cl (R = i-Pr (14), t-Bu (15)), and Cp*Zr(NPR3)(CH2C(CH3)C(CH3)CH2) (R = i-Pr (16), t-Bu (17)). Reaction of 17 with the borane B(C6F5)3 yielded the zwitterionic and cationic complexes Cp*Zr(NP-t-Bu3)(CH2C(CH3)C(CH3)CH2B(C6F5)3) (18) and Cp*Zr(NP-t-Bu3)(THF)(CH2C(CH3)C(CH3)CH2B(C6F5)3) (19). A number of the above compounds were screened for their potential as catalyst precursors in ethylene polymerization. In general, upon activation with methylaluminoxane, the resulting catalysts exhibit low activity. Efforts to understand the deactivation pathway for these zirconium catalysts involved investigating the interactions of catalyst precursors with activators. For example, reaction of 4 with the borane B(C6F5)3 leads to aryl group transfer and formation of catalytically inactive CpZr(NP-t-Bu3)(C6F5)2 (20). Interactions with MAO were modeled via reaction with AlMe3. The Zr clusters (Cp*Zr)4(μ-Cl)5(Cl)(μ-CH)2 (21) and (Cp*Zr)5(μ-Cl)6(μ-CH)3 (22) were two of the products that were characterized from these reactions. The isolation of 21 and 22 infers that aryl for methyl exchange, ligand abstraction, and C−H bond activation may be catalyst deactivation pathways.

The compounds (indenyl)Ti(NP-t-Bu3)Cl2 (4), Cp2Ti(NP-t-Bu3)Cl (6), (indenyl)2Ti(NP-t-Bu3)Cl (7), Cp(indenyl)Ti(NP-t-Bu3)Cl (8), Cp3Ti(NP-t-Bu3) (9), (indenyl)3Ti(NP-t-Bu3) (10), and Cp(indenyl)2Ti(NP-t-Bu3) (11) are readily derived from reaction with (dme)NaCp or Li(indenyl) with CpTi(NP-t-Bu3)Cl2 (1) or 4 in the appropriate stoichiometry. X-ray crystallography studies of (indenyl)Ti(NP-t-Bu3)Me2 (5) and 7−11 are reported. In the case of 6 and 9 two cyclopentadienyl rings are bound to the metal in a η⁵ -bonding mode, whereas in 7, 8, 10, and 11 one of the cyclopentadienyl or indenyl ligands is bound in an η⁵ mode and the remainder in an η¹-fashion. In the case of 10, temperature-dependent ¹H NMR spectra infer a η⁵-η¹ ligand exchange process with an approximate barrier of 8−9 kcal/mol. Steric crowding appears to be the major factor determining the binding modes of the cyclopentadienyl and indenyl ligands. These structural data result in a view of the phosphoraneiminato ligand as a sterically demanding, four-electron donor ligand.

The phosphinimide−phosphines PPh2(NPR3) (R = i-Pr 1, t-Bu 2) were readily prepared in 80−98% yield. These species react with AlMe3 or B(C6F5)3 to form Me3AlPPh2(NPR3) (R = i-Pr 3, t-Bu 4) and (C6F5)3B(PPh2(NPi-Pr3)) (5), respectively. Oxidation of compounds 1 and 2 with Me3SiN3 yields Me3SiNPPh2(NPR3) (R = i-Pr 6, t-Bu 7). These species react with CpTiCl3 to give titanium(IV) complexes CpTiCl2(NPPh2(NPR3) (R = i-Pr 8, t-Bu 9) and subsequently the alkylated complexes CpTiMe2(NPPh2(NPR3)) (R = i-Pr 10, t-Bu 11). Compounds 8−11 were tested for activity in ethylene polymerization. In the presence of excess methylalumoxane, the species 8 and 9 gave rise to active single-site catalysts, generating 299 and 34 gPE mmol^-1 h^-1, respectively. In contrast, activation of 10 and 11 by [Ph3C][B(C6F5)4] showed negligible polymerization activity. Reaction of 11 with B(C6F5)3 was shown to give numerous products, one of which was the dicationic species [CpTi(μ-Cl)(NPPh2(NPt-Bu3)]2[BC6F5)4]2, 12. The formation of this species and the implications of these results for catalyst and ancillary ligand design are considered and discussed. X-ray crystallographic data are reported for 1, 3, 4, 8, and 12.

This paper focuses on the synthesis and reactivity of Cp*Ta(V)−phosphinimide complexes. Reaction of stoichiometric mixtures of Cp*TaCl4 and phosphinimine R3PNSiMe3 affords the complexes Cp*Ta(NPR3)Cl3, R = t-Bu 1, i-Pr 2. These species are readily derivatized to the alkylated complexes Cp*Ta(NPR3)Me3, R = t-Bu 3, i-Pr 4; Cp*Ta(NPt-Bu3)(CH2Ph)Cl2, 5; and Cp*Ta(NPt-Bu3)(CH2Ph)Me2, 6. Reaction with 3 equiv of BnMgCl afforded the robust alkylidene species Cp*Ta(NPR3)(CHPh)(CH2Ph), R = t-Bu 7, i-Pr 8. Reaction of 7 with MeI gives the metallacycle Cp*Ta(NPt-Bu3)(η²-CHPhCH2)(CH2Ph), 9. Alkylation of 1 and 2 with 2 equiv of EtMgCl results in formation of the complexes Cp*Ta(NPR3)(η²-C2H4)Cl, R = t-Bu 10, i-Pr 11, while further reaction of 10 with EtMgCl affords Cp*Ta(NPt-Bu3)(η²-C2H4)(CH2CH3), 12. Reaction of 1 with 1 equiv of B(C6F5)3 results in generation of the salt [Cp*Ta(NPt-Bu3)Cl2][ClB(C6F5)3], 13, while the analogous reaction with Ph3C[B(C6F5)4] affords the related salt [Cp*Ta(NPt-Bu3)Cl2][B(C6F5)4], 14. The zwitterionic species Cp*Ta(NPR3)Me2(MeB(C6F5)3) (R = t-Bu 15, i-Pr 16) are derived via reaction of 3 or 4 with B(C6F5)3. The analogous reaction of 3 and 4 with [Ph3C][B(C6F5)4] affords the related salts [Cp*Ta(NPR3)Me2][B(C6F5)4] (R = t-Bu 17, i-Pr 18). Treatment of 10 with Ph3CB(C6F5)4, Ph3CBF4, or B(C6F5)3 gives the complexes [Cp*Ta(NPt-Bu3)(Cl)CH2CH2CPh3][B(C6F5)4], 20, [Cp*Ta(NPt-Bu3)(Cl)(CH2CH2CPh3)][BF4], 21 and the zwitterionic species [Cp*Ta(NPt-Bu3)(Cl)(CH2CH2B(C6F5)3)], 22, respectively. The relevance of this chemistry to the related group IV metal olefin polymerization catalysts is discussed and considered. X-ray structural studies of 1, 3, 5, 7, 9, 10, and 22 are reported.

Multiple C−H bond activation occurs upon reaction of phosphinimide complexes of the form Cp‘(R3PN)TiMe2 (Cp‘ = Cp, indenyl; R = i-Pr, Cy, Ph) with excess AlMe3, affording the carbide complexes Cp‘Ti(μ²-Me)(μ²-NPR3)(μ⁴-C)(AlMe2)3 or in some cases [CpTi(μ²-Me)(μ²-NPR3)(μ⁵-C)(AlMe2)3·(AlMe3)]. These species contain four- and five-coordinate carbide centers. VT-NMR studies established that such species exist in equilibrium. The four-coordinate carbide complexes retain Lewis acidity at a planar three-coordinate Al center, as evidenced by the reaction with diethyl ether, THF, or PMe3. This affords species of the form [CpTi(μ²-Me)(μ²-NPR3)(μ⁴-C)(AlMe2)2(AlMe2(L))] (L = Et2O, THF, PMe3). The Lewis acidity is also evidenced in the reaction of the carbide complexes with CpTi(NPR3)Me2. In this case, labeling studies affirm methyl group exchange processes. The analogous reactions of Cp(R3PN)Ti(CH2SiMe3)2 or Cp*(R3PN)TiMe2 with AlMe3 afforded CpTi(μ²-Me)(μ²-NPR3)(μ³-CSiMe3)(AlMe2)2 and Cp*Ti(μ²-Me)(μ²-NPR3)(μ³-CH)(AlMe2)2, respectively. These observations confirm that steric congestion can impinge on the C−H activation process. The nature of the above products of C−H bond activation was confirmed employing NMR, isotopic labeling, and crystallographic methods. The implications of these results with respect to C−H bond activation and polymerization catalysis are considered.

The known ligand PPh(C6H4O3Me4) (1) and its analogue PCy(C6H4O3Me4) (2) have been prepared. In the latter synthesis the diphosphine species (PCy)2(C6H2O3Me4) (3) was also isolated as a minor product. Reaction of the cage phosphines 1 and 2 with Me3SiN3 effected oxidation to the corresponding (trimethylsilyl)phosphinimines Me3SiNPR(C6H4O3Me4) (R = Ph (4), Cy (5)). Subsequent reactions afforded the titanium complexes CpTiCl2(NPR(C6H4O3Me4)) (R = Ph (6), Cy (7)) and CpTiMe2(NPR(C6H4O3Me4)) (R = Ph (8), Cy (9)). Preliminary screening for catalytic activity in ethylene polymerization employing either methylalumoxane (MAO) or [Ph3C][B(C6F5)4] as the activator showed minimal catalytic activity. These observations were probed via reactions of these complexes with AlMe3, MAO, or [Ph3C][B(C6F5)4]. Reaction of 8 with AlMe3 gave several products, one of which was fully characterized as the cage-rupture product CpTiMe2(NPCy(C6H4O3Me5)(μ-AlMe2)(AlMe3)) (10). A similar product is inferred by the spectroscopic monitoring of the reaction of 8 with MAO. In contrast, reaction of 2 with AlMe3 resulted only in the formation of the adduct Me3AlPCy(C6H4O3Me4) (11). Structural data are reported for 2, 3, 8, 10, and 11.

The phosphinimide complexes (t-Bu3PN)TiCl3 (1) and (t-Bu3PN)2TiCl2 (4) are readily prepared in high yields from the stoichiometric reaction of t-Bu3PNSiMe3 and TiCl4, while (t-Bu3PN)3TiCl (11) is readily obtained from the reaction of t-Bu3PNLi and TiCl4. The analogous 1:1 or 2:1 reactions of ZrCl4 and t-Bu3PNLi afford mixtures of products, although in the 3:1 stoichiometric ratio (t-Bu3PN)3ZrCl (12) is isolable. These complexes are readily alkylated with a variety of reagents to give (t-Bu3PN)TiMe3 (2), (t-Bu3PN)Ti(CH2Ph)3 (3), (t-Bu3PN)2TiMe2 (5), (t-Bu3PN)2Ti(η³-C3H5)2 (6), (t-Bu3PN)2Ti(CH2Ph)2 (7), (t-Bu3PN)2TiPh2 (8), (t-Bu3PN)2Ti(η⁵-Cp)Cl (9), (t-Bu3PN)2Ti(η⁵-Cp)Me (10), (t-Bu3PN)3TiMe (13), (t-Bu3PN)3TiPh (14), (t-Bu3PN)3ZrMe (15), (t-Bu3PN)3Zr(CH2Ph) (16), and (t-Bu3PN)3Zr(η⁵-Cp) (17). Subsequent reactions of some of these alkyl derivatives with [PhNMe2H][B(C6F5)4], [Ph3C][B(C6F5)4], or B(C6F5)3 are investigated. A number of zwitterionic and cationic species complexes have been characterized. These include [(t-Bu3PN)Ti(CH2Ph)2(PhCH2)B(C6F5)3] (18), [(t-Bu3PN)2TiMe(PMe3)][B(C6F5)4] (19), (t-Bu3PN)2TiMe (μ-MeB(C6F5)3) (20), (t-Bu3PN)2Ti(μ-MeB(C6F5)3)2 (21), and (t-Bu3PN)2Ti(C6F5)2 (22). The implications of this chemistry are considered. Structural data for 1, 4, 5, 12, 16, 21, and 22 are described.

The reactions of [(C5Me5)2ZrH3Li]3 (1) with 2,6-diisopropylphenol, aniline, and o-methoxyaniline gave Cp*2ZrH(OC6H3(2,6-i-Pr2)) (2), Cp2*Zr(NHPh)2 (3), and Cp2*Zr(NH(C6H4OMe))2 (4), respectively. In contrast, reaction of 1 with thiophenol afforded [(Cp*2ZrH3)(LiTHF)]2(LiSPh) (5). The implications of these results are considered. Crystallographic data for 3−5 are reported.

Stoichiometric reaction of [(C5Me5)2ZrH3]Li (1) with diphenylphosphine sulfide or selenide yields the bimetallic species [(C5Me5)2ZrH]2(μ-E) (E = S 2, Se 3). These reactions are proposed to proceed via an intermediate of the form [(C5Me5)2ZrH2(EPPh2)]^- with concurrent loss of dihydrogen. Subsequent β-elimination of Ph2PH affords 2 and 3 via dimerization and loss of Li2E. The initial synthetic strategy to trap an anionic intermediate involved treatment of 1 with diphenylphosphine oxide. This approach failed, affording instead the tetrameric species [Ph2POLi(THF)]4 (4) and Cp*2ZrH2. An alternative, successful approach to an oxide anion involved the reaction of 1 with Me3NO. The resulting species [(C5Me5)2ZrH(OLi(THF))]2 (5) was isolated, and the species 2−5 have been structurally characterized. These results are presented and the implications discussed.

Reactions of the silylphosphimines R3PNSiMe3 (R = i-Pr, Ph, Cy) with AlCl3, AlMeCl2, AlMe2Cl, and AlMe3 afford the compounds (i-Pr3PNSiMe3)AlCl3 (1), (R3PNSiMe3)AlMeCl2 (R = i-Pr, 2; Ph, 3; Cy, 4), (R3PNSiMe3)AlMe2Cl (R = i-Pr, 5; Ph, 6; Cy, 7), and (R3PNSiMe3)AlMe3 (R = i-Pr, 8; Ph, 9; Cy, 10). Reaction of R3PNH (R = t-Bu, Cy, Ph) with AlMe2Cl and AlMe3 afforded (R3PNH)AlMe2Cl (R = Cy, 11; t-Bu, 12) and (Ph3PNH)AlMe3 (13), respectively. The dimeric species [Me2Al(μ-NPt-Bu3)]2 (14) [AlCl2(μ-NPt-Bu3)]2 (15) were derived from reactions of (t-Bu3PNH) and AlMe3 and t-Bu3PNLi and MeAlCl2, respectively. Reaction of the bisphosphinimine salt LiCH(PPh2(NSiMe3))2 (16) with aluminum, gallium, and indium halides yielded [CH(PPh2(NSiMe3))2]MCl2 (M = Al, 17; Ga, 18; In, 19) while the analogous species [CH(PPh2(NSiMe3))2]AlMe2 (20) was prepared via reaction of 16 with Me2AlCl. The compounds [CH(PPh2(NSiMe3))2]MR2 (M = Al, Bz, 21; M = Ga, R = Me, 22; Bz, 23; M = In, R = Me, 24; Bz, 25) were readily prepared by treatment of 17−19 with the appropriate alkylating reagents. The borane B(C6F5)3 reacts stoichiometrically with the adducts 8−10 to give the products [(R3PNSiMe3)AlMe2][MeB(C6F5)3] (R = i-Pr, 26; Ph, 27; Cy, 28) while treatment of 27 with PMe3 affords clean conversion to the salt [(Ph3PNSiMe3)2AlMe(PMe3)][(MeB(C6F5)3)] (29). Similarly, species [Me2Al(μ-NPt-Bu3)2AlMe][MeB(C6F5)3] (30) and [Me2Al(μ-NPt-Bu3)2AlMe(PMe3)][MeB(C6F5)3] (31) were obtained from 14. Attempts to generate the related ionic derivatives from 20−25 yielded unstable mixtures of products. Under mild conditions these group 13 ionic species did not effect the polymerization of ethylene. Crystallographic data are reported for compounds 1, 3, 6, 8, 11, 13−15, 18, and 20.

The employment of phosphazirconacycles in metallacycle transfer reactions is a facile method for the synthesis of main-group phosphacycles. Reactions of Cp2Zr(PPh)3 (1), Cp2Zr(P(R*)C(Ph)&dbd;CPh) (2), and Cp2Zr(P(Mes)P(Mes)C(Ph)&dbd;CPh) (3) with various main-group dihalides results in cleavage of TM−MG bonds and formation of new MG−MG bonds. Triphosphanato complex 1 reacts with PhPCl2 or ^tBu2SnCl2 to yield (PPh)4 (4) and (t-Bu)2Sn(PPh)3 (7), respectively. Reaction of phosphametallacyclobutene 2 with PhPCl2 results in the formation of the unsymmetrically substituted 1,2-diphosphetene P(Ph)P(R*)C(Ph)&dbd;CPh (5), while reaction with PhBCl2 yields PH(C6H2-(2-CH2C(CH3)2)-4,6-t-Bu2)B(Ph)CPh&dbd;CPh (8), the product of ring expansion via C&sbd;H activation. Phosphametallacyclopentene 3 reacts with PhPCl2 to furnish the unsymmetrically substituted 1,2,3-triphospholene P(Ph)P(Mes)P(Mes)C(Ph)&dbd;CPh (6). Advantages to such metallacycle transfer reactions include (i) facile accessibility of main-group derivatives where conventional syntheses are laborious, tedious, and/or fraught with safety issues, (ii) selective control over molecular fragments, and (iii) new routes to novel main-group compounds.

Elimination of methane from Cp2Zr(PR*H)(Me) (R* = C6H2-2,4,6-t-Bu3) (4) in the presence of diphenylacetylene or phenylpropyne afforded the [2 + 2] cycloaddition products Cp2Zr(P(R*)C(Ph)&dbd;CPh) (3) and Cp2Zr(P(R*)C(Me)&dbd;CPh) (5), respectively. Alternatively, the [2 + 2] cycloaddition reaction between (Cp2Zr&dbd;PR*)(PMe3) (1) and phenylacetylene yielded Cp2Zr(P(R*)C(H)&dbd;CPh) (6). Metallacycles 3 and 5 undergo facile [2 + 2] retrocycloaddition reactions; addition of 1 equiv of phenylpropyne to 3 resulted in an equilibrium mixture of 3 and 5. In contrast, addition of phenylacetylene to 3 yielded Cp2Zr(C&tbd1;CPh)(C(Ph)&dbd;C(Ph)PHR*) (7), the product of C&sbd;H activation of the terminal alkyne. Attempts to synthesize a phosphametallacycle with less sterically hindered substituents on phosphorus by reaction of Cp2ZrMeCl, diphenylacetylene, and LiHPMes (Mes = C6H2-2,4,6-Me3) instead led to the formation of Cp2Zr(P(Mes)P(Mes)C(Ph)&dbd;CPh) (8). Probing the mechanism of formation of 8 by reaction of (Cp2ZrCl)2(μ-PMes) with Li2PMes in the presence of diphenylacetylene afforded Cp2Zr(P(Mes)C(Ph)&dbd;CPh) 9. However, reaction of 9 with H2PMes instead resulted in the formation of the unstable compound Cp2Zr(C(Ph)&dbd;C(Ph)PMesH)(PMesH) (10). Phosphametallacyclobutene 3 reacts with tert-butyl isocyanide, acetone, cyclohexanone, benzonitrile, benzaldehyde and styrene oxide to give the insertion products Cp2Zr(C(&dbd;N-t-Bu)P(R*)C(Ph)&dbd;CPh) (12), Cp2Zr(OCMe2P(R*)C(Ph)&dbd;CPh) (13), Cp2Zr(O(c-CC5H10)P(R*)C(Ph)&dbd;CPh) (14), Cp2Zr(N&dbd;C(Ph)P(R*)C(Ph)&dbd;CPh) (15), Cp2Zr(OCHPhP(R*)C(Ph)&dbd;CPh) (16), and Cp2Zr(OCH2CHPhP(R*)C(Ph)&dbd;CPh) (17), respectively. Compounds 16 and 17 were also obtained by reaction of either benzaldehyde or styrene oxide with 13, 14, or 15, via [4 + 2] retrocycloadditions. Epimerization at phosphorus has been identified in complexes 3, 5, 6, 8, 9, and 12−15, and has been attributed to steric congestion in these species. Spectroscopic methods, X-ray crystallography, and molecular orbital calculations have been employed to address this issue.

The reaction of Cp2ZrMe(PHR) with benzophenone, cyclohexanone, acetone, benzaldehyde, and benzophenone results in the insertion of the organic substrate into the Zr−P bond. In this way, the complexes Cp2ZrMe(OCPh2PH(C6H2-2,4,6-t-Bu3)) (3), Cp2ZrMe(OC6H10PH(C6H2-2,4,6-t-Bu3)) (4), Cp2ZrMe(OCMe2PHR) (R = (C6H2-2,4,6-t-Bu3) (5), R = (C6H2-2,4,6-Me3) (8), and Cp2ZrMe(NC(Ph)PH(C6H2-2,4,6-t-Bu3)) (6) were prepared. The species Cp2ZrMe(PH(C6H2-2,4,6-Me3)) (7) was also formed in the reaction of Cp2ZrMe2 with H2P(C6H2-2,4,6-Me3); however, 7 reacted further with Cp2ZrMe2 to give the bimetallic species (Cp2ZrMe)2(μ-P(C6H2-2,4,6-Me3) (9). In the analogous reaction of Cp2ZrMe2 with 1 equiv of H2P(C6H2-2,4,6-Me3), the species (Cp2Zr)(Cp2ZrPH(C6H2-2,4,6-Me3))(μ-P6H2-2,4,6-Me3))(μ-η¹-η⁵-C5H4) (11) was obtained. Compound 11, which results from cyclopentadienyl C−H bond activation, was also formed directly from degradation of the unstable terminal phosphinidene species Cp2Zr(P(C6H2-2,4,6-Me3))(PMe3) (12). The implications of this chemistry are considered and discussed. Compound 3, 9, and 11 have been characterized crystallographically.

1,2-disubstituted cyclopentadienyl diimine anions are examples of extended π-systems that bind metals through the nitrogen atoms. Reaction of Cp2Mg with benzonitrile gives the product (1,2-C5H3(C(Ph)NH)2)CpMg(NCPh) (1) in 98% yield. In an analogous manner, the related complexes (1,2-C5H3(C(Ph)NH)2)CpMg(OEt2) (2) and ((4-Me3SiC5H2)(1,2-(C(Ph)NH)2)(Me3SiC5H4)Mg(OEt2) (3) were prepared in situ. Demetalation of these complexes 1−3 yields the corresponding free diimine ligands of formulation H[(1,2-C5H3(C(Ph)NH)2)] (4) and H[4-Me3SiC5H2-1,2-(C(Ph)NH)2] (5). Hydrolysis of compound 4 leads to the fulvene derivative 1-(C(OH)Ph)-2-(O&dbd;C(Ph))C5H3 (6). The zirconium complexes (C5H3-1,2-(C(Ph)NH)2)ZrCl3(THF) (7) and (C5H3-1,2-(C(Ph)NH)2)3ZrCl (8) were isolated from reactions of 4 with ZrCl4(THF)2. X-ray crystallographic studies of 1, 7, and 8 are reported. Evidence suggests that these new 1,2-disubstituted cyclopentadienyl diimine anions impart some charge delocalization, thus offering a new approach to electrophilic metal centers. This view is supported by EHMO calculations.

The thermolysis of monocyclopentadienyltitanium thiolate complexes leads to ligand redistributions and C−S bond cleavage reactions. Kinetic study of the C−S bond thermolysis reaction of CpTi(OC6H3-2,6-i-Pr2)(SBn)2 (2) to the sulfide-bridged dimer [CpTi(OC6H3-2,6-i-Pr2)(μ-S)]2 (1) is shown to be first order in 2, consistent with an intramolecular process proceeding via a terminal sulfide intermediate and rapid dimerization (k = 2.8 × 10^-6 s^-1). The related species CpTi(OC6H3-2,6-i-Pr2)(SBn)Cl (3), CpTi(OC6H3-2,6-i-Pr2)(SMe)2 (4), and CpTi(OC6H3-2,6-i-Pr2)(SPh)2 (5) are thermally stable, although compounds 4 and 5 undergo thermally induced ligand redistribution reactions. These redistribution reactions are thought to occur via a dimeric intermediate in which bridging thiolate ligands are exchanged between two metal centers. A dimeric intermediate is supported by the characterization of the species [CpTi(SR)2(μ-SR)]2 (R = Et (7), Bn (8)) which are dimeric in solution at low temperature and in the solid state. In contrast, Cp*Ti(SBn)3 (9) is monomeric. Efforts to intercept a terminal sulfide intermediate in the formation of 1 were unsuccessful, although reaction of CpTiCl2Me with LiSBn in the presence of PMe3 gives [CpTiCl(μ-S)]2[PMe3Bn] (10) in low yield. The analogue of 2, Cp*Ti(OC6H3-2,6-i-Pr2)(SBn)2, 12, is thermally stable; however, thermolysis of Cp*TiCl(SBn)2 gave [Cp*TiCl(μ-S)]2 (13). Ultimately, the LiCl adduct of a terminal sulfide species Cp*Ti(OC6H3-2,6-i-Pr2)(μ-S)(μ-Cl)Li(THF)2 (14) was isolated from the reaction of Cp*Ti(OC6H3-2,6-i-Pr2)Cl2 (11) with Li2S. Treatment of (14) with PMe3 generates the monomeric terminal sulfide complex species Cp*Ti(OC6H3-2,6-i-Pr2)(S)(PMe3) (15), which is unstable, slowly evolving PMe3 affording [Cp*Ti(OC6H3-2,6-i-Pr2)(μ-S)]2 (16). Compound 16 is also obtained directly by heating solutions of 14. Crystallographic studies of 8, 10, 12, 13, 14, and 16 are reported herein. The intermediacy of terminal metal sulfides in C−S processes are discussed.

The reactions of Cp2MH3 (M = Nb, Ta) or Cp‘2NbH3 (Cp‘ = Me3SiC5H4) with excess primary phosphines yield the complexes Cp2NbH[(PPh)2] (1), Cp‘2NbH[(PPh)2] (2), and Cp2TaH[(PR)2] (R = Ph, 3; R = Cy, 4). Crystallographic studies of each of these compounds confirmed the transoid disposition of the phosphorus substituents with respect to the MP2 ring. Reaction of Cp2TaH3 with white phosphorus afforded the parent complex Cp2TaH[(PH)2] (5). While crystallographic characterization of 5 confirmed the formulation, it failed to reveal the orientation of the hydrogen atoms on P. Variable temperature NMR studies in conjunction with selective decoupling, 2D, NOE, and NOESY experiments were performed on compound 5. These experiments were consistent with a transoid disposition of the hydrogens atoms on P at low temperature. The marked temperature dependence of the NMR data, while suggestive of a fluxional process, is more logically explained in terms of a dramatic and unusual temperature dependence of the ³¹P chemical shifts. These results are discussed and their implications considered.

The thiolate complexes CpTi(OC6H3-2,6-i-Pr2)(SR)Cl (R = Et, 1; t-Bu, 2; CH2Ph, 3; Ph, 4) were prepared. Attempts to methylate 1−4 and thus obtain the potentially reactive alkyltitanium thiolate derivatives were unsuccessful. Thiolation of CpTi(OC6H3-2,6-i-Pr2)(Me)Cl (5) with 1,1-dimethylethanethiol in the presence of base afforded the species CpTi(OC6H3-2,6-i-Pr2)(Me)(SCMe3) (6). The analogous species CpTi(OC6H3-2,6-i-Pr2)(Me)(SCH2Me) (7) is unstable, liberating methane and yielding the dimeric product of C−H bond activation, [CpTi(OC6H3-2,6-i-Pr2)(μ-SCHMe)]2 (8). In a related thermolysis of CpTi(OC6H3-2,6-i-Pr2)(SBn)2 (9), the dimer species [CpTi(μ-S)(OC6H3-2,6-i-Pr2)]2 (10) and (PhCH2)2S are obtained. In contrast, thermolysis of the closely related species CpTi(OC6H3-2,6-i-Pr2)((SCH2)2C6H4) (11) and CpTi(OC6H3-2,6-i-Pr2)(SCH2Me)2 (12) resulted in no reaction, suggesting a radical process is operative in the formation of 10. Reduction of 2 with LiPCy2 gave (PCy2)2 and the S−C bond cleavage product [CpTi(OC6H3-2,6-i-Pr2)(μ³-S)]3TiCp (13). These pathways of C−H and C−S bond activation are discussed and the implications considered.

Additions of PhEH (E = O, S), PhEH2 (E = N, P), MesPH2, and Ph2PH to Cp2Zr(PR*)(PMe3) (2) provide a facile route to complexes of the form Cp2Zr(PHR*)(ER) (R* = 2,4,6-t-Bu-C6H2; ER = OPh (3), SPh (4), NHPh (5), PHPh (6), PHMes (7), PPh2 (8)). Variable-temperature NMR studies are consistent with facile metal-mediated inversion at phosphorus as well as rapid rotation about the Zr−E bonds at room temperature.

The complexes [Cp^†Ti(SCHCH2CH2S)]2 (Cp^† = Cp (3), MeCp (4)) are readily prepared from reaction of Cp^†Ti(SCH2CH2CH2S)Cl (Cp^† = Cp (1), MeCp (2)) with MeLi, AlMe3, or t-BuLi. Both compounds are centrosymmetric dimers in the solid state containing strained thiatitanacyclopropane rings. PMe3 cleaves these dimers, establishing equilibria between 3 and 4 and Cp^†Ti(SCHCH2CH2S)(PMe3) (Cp^† = Cp (5), MeCp (6)), while compound 3 undergoes facile acidolysis with HCl, acetic acid, PhSH, and propanedithiol affording CpTiCl3, CpTi(O2CMe)3 (7), CpTi(SCH2CH2CH2S)(SPh), and H⁺[CpTi(SCH2CH2CH2S)2]^-·THF (8), respectively. The thiametallacycles react with benzophenone to give Cp^†Ti(SCH(CPh2O)CH2CH2S) (Cp^† = Cp (9); MeCp (10)) while reaction with cyclohexanone gives the dimeric species [Cp^†Ti(SCH(C6H10O)CH2CH2S)]2 (Cp^† = Cp (11); MeCp (12)). Analogous reactions with 2-methylcyclohexanone, menthone, and nopinone give related addition products with varying degrees of diastereoselectivity. The complex 3 also reacts with a series of imines to give complexes of the form CpTi(SCH(CHRNR)CH2CH2S), where the diastereoselectivity observed is a function of the steric demands of the substrate substituents. Reaction of 3 with nitriles, methyl isocyanate, dicyclohexylcarbodiimide, and phenyl thioisocyanate results in insertion of the substrate and subsequent enolization to give species of the form CpTi(SC=(C(R)NH)CH2CH2S). The analogous reaction with phenyl isocyanate yields the bimetallic complex CpTi(SC(PhNCO)CH2CH2S)TiCp(SCH2CH2CH2S) (27). Crystallographic characterization of a number of these reaction products is reported. Kinetic studies of the formation of 10 and 12 are consistent with initial formation of ketone complex adducts and subsequent intra- and intermolecular C−C bond formation reactions. The nature of the products, reaction mechanisms, and reactivity of strained thiatitanacyclopropane rings are discussed in the light of EHMO calculations.

Reactions of (Cp*CrCl2)2 (1) and Cp*Cr(HNP-i-Pr3)Cl2 (3) with excess AlMe3 gave [(Cp*Cr)4(μ-Cl)3(μ-CH2)3AlMe][(Me2Al)(μ3-O)(AlCl2Me)(AlMe2Cl)] (2) and [(Cp*Cr)4(μ-Cl)3(μ-CH2)3AlMe][(Me2Al)2(μ-CH)(AlCl2Me)2] (4), respectively. Although the cations are the same, the former salt has a Al3O-based anion, whereas the latter contains an Al4−methine anion.

The species [(HC(PPh2NSiMe3)2Cr(μ-Cl)2] was prepared and structurally characterized. It is shown to exist in two structural isomers:  one in which the Cr center adopts a pseudo-square-planar coordination geometry and another where the metal coordination sphere is better described as trigonal bipyramidal. Preliminary assessment of the catalytic activity in ethylene polymerization is also reported.