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The use of the diolate ligand derived from the deprotonation of 2,2'-methylenebis(6-tert-butyl-4-methylphenol) abbreviated as HO-CH2-OH was discussed. The nature of interconversion of bridged and chelate isomers in the presence of Lewis bases was established. The reaction of MO2(NMe2)6 and HO-CH2-OH yielded MO2(NMe2)2(O-CH2-O)2, which exists in both bridged and chelate isomers. The first example of reversible C-H oxidative addition to M-M multiple bond was observed and monitored.

Propynylidene 1 (HCCCH) is the simplest alkynylcarbene that, along with abundant interstellar cyclopropenylidene 2 and propadienylidene 3 has attracted substantial interest. The propynylidene can be generated as an organodimetallic ligand in solution by double C-H activation of allene and it can adopt a curved structure.

A series of lithium and sodium complexes with OOO-tridentate bis(phenolate) ligands have been synthesized and fully characterized. The reaction of 2,2'-dihydroxy-3,3',5,5'-tetrakis[(1-methyl-1-phenyl)ethyl]dibenzyl ether (L(1)-H(2)) with different ratios of (n)BuLi in toluene or tetrahydrofuran (THF) gave [Li(2)(L(1)-H)(2)] (1), [Li(4)L(1)(2)] (2), and [Li(2)L(1)(THF)(3)] (3), respectively. Similarly, [Na(L(1)-H)(THF)] (4), [Na(2)(L(1)-H)](2) (5), and [Na(4)L(1)(2)] (6) were prepared by the reaction of L(1)-H(2) and NaN[Si(CH(3))(3)](2) or sodium metal. In addition, the reaction of 2,2'-dihydroxy-3,3',5,5'-tetra-tert-butyldibenzyl ether (L(2)-H(2)) with (n)BuLi in toluene or THF yields Li(2)(L(2)-H)(2)] (7) and [Li(2)(L(2)-H)(2)(THF)(2)] (8), respectively. Further treatment of 7 with 2 mol equiv of benzyl alcohol provides [Li(2)(L(2)-H)(2)(BnOH)(2)] (9). Complexes 1-4 and 6-9 have been structurally characterized by single-crystal X-ray analysis. The dinuclear nature of complexes 1 and 3 was confirmed from their molecular structure. Complexes 2 and 6 illustrate tetranuclear species; however, complex 4 shows a mononuclear feature. A p-π interaction exists from the phenyl ring of the 2-(methyl-1-phenylethyl) groups to the central metal in complexes 2, 4, and 6, which could effectively stabilize the metal center. Among them, complexes 1, 2, and 5-9 displayed efficient catalytic behavior for the ring-opening polymerization of L-lactide in the presence of benzyl alcohol. Experimental results indicate that among these alkali-metal complexes, the sodium compound 6 displays a rapid catalytic polymerization of L-lactide in "living" fashion, yielding poly(L-lactide) with a controlled molecular weight and narrow polydispersity indices for a wide range of monomer-to-initiator ratios.

The new pyrrolyl-linked pincer-type ligand, [C(4)H(2)NH(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))] (1), that has been employed conveniently in high yield by treatment of (2-t-butylaminomethyl)pyrrole with 1 equiv of formaldehyde and dimethylamine hydrochloride each in diethylether and its corresponding aluminum derivative, [C(4)H(2)N(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))]AlH(2) (2), that has been generated from Me(3)N.AlH(3) using diethylether as a solvent are described. Furthermore, reactions of 2 with 2 equiv of either 1,3-diphenylpropane-1,3-dione in diethylether or phenyl thioisocyanate in dichloromethane interestingly formed [C(4)H(2)N(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))]Al(PhCOCHCOPh)(2) (3) and [C(4)H(2)N(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))]Al(SCHNPh)(2) (4), respectively, following deprotonation or hydroalumination reaction kinetics under a dry nitrogen environment. All of the compounds have been subjected to the X-ray diffraction technique in the solid state as well as characterized by NMR spectra.

A series of monomeric, dimeric, and trimeric calcium compounds containing substituted pyrrolyl or ketiminate ligands were synthesized, and characterized by NMR spectroscopy and single crystal X-ray diffractometry. The reaction of Ca[N(SiMe(3))(2)](2)(THF)(2) with 1 equiv of [C(4)H(3)NH(2-CH(2)NEt(2))] in toluene generates the dimeric complex, [Ca{N(SiMe(3))}[mu-eta(1):eta(5)-{C(4)H(3)N(2-CH(2)NEt(2))}]](2) (1) in which two substituted pyrrolyl ligands bind two Ca centers in a eta(1) and eta(5) fashion. The reaction between Ca[N(SiMe(3))(2)](2)(THF)(2) and 2 equiv of [C(4)H(3)NH(2-CH(2)NEt(2))] in THF yields a monomeric calcium compound Ca[C(4)H(3)N(2-CH(2)NEt(2))](2)(THF)(2) (2) that exhibits a facial octahedral geometry on the central Ca atom. Similarly, the reactions of Ca[N(SiMe(3))(2)](2)(THF)(2) with 1 and 2 equiv of OCMeCHCMeNHAr (Ar = 2,6-diisopropylphenyl) generate [Ca(OCMeCHCMeNAr){N(SiMe(3))(2)}](2) (3) and [Ca(mu-OCMeCHCMeNAr)(OCMeCHCMeNAr)](2) (4), respectively. In 3, the Ca atom possesses a distorted tetrahedral geometry where as in 4, a square plane is developed by the two calcium atoms with the bridging participation of two oxygen atoms from two ketiminate ligands. The in situ reaction of OCMeCHCMeNHAr, Ca[N(SiMe(3))(2)](2)(THF)(2), and isopropyl alcohol results in a trimeric calcium alkoxide compound Ca(3)(mu-OCMeCHCMeNAr)(2)(OCMeCHCMeNAr)(mu(3)-O-(i)Pr)(2)(mu(2)-O-(i)Pr) (5). Compounds 1, 2, and 5 showed good catalytic activity in the ring-opening polymerization of epsilon-caprolactone and l-lactide.

Treatment of (t-)BuN=TiCl(2)Py(3) with 2 equiv lithium ketiminate compound, Li[OCMeCHCMeN(Ar)] (where Ar = 2,6-diisopropylphenyl), in toluene at room temperature gave (t-)BuN=Ti[OCMeCHCMeN(Ar)](2) (1) in high yield. The reaction of 1 with phenyl isocyanate at room-temperature resulted in imido ligand exchange producing PhN=Ti[OCMeCHCMeN(Ar)](2) (2). Compound 1 decomposed at 90 degrees C to form a terminal titanium oxo compound O=Ti[OCMeCHCMeN(Ar)](2) (3) and (t-)BuNHCMeCHCMeNAr (4). Also, the compound 3 could be obtained by reacting 1 with CO(2) under mild condition. Similarly, while 1 reacts with an excess of carbon disulfide, a novel terminal titanium sulfido compound S=Ti[OCMeCHCMeN(Ar)](2) (5) was formed via a C=S bond breaking reaction. A novel titanium isocyanate compound Ti[OCMeCHCMeN(Ar)](2)(NCO)(OEt) (6) was formed on heating 1 with 1 equiv of urethane, H(2)NCOOEt. Compounds 1-6 have been characterized by (1)H and (13)C NMR spectroscopies. The molecular structures of 1, 3, 5, and 6 were determined by single-crystal X-ray diffraction. A theoretical calculation predicted that the cleavage of the C-S double bonds for carbon disulfide with the Ti=N bond of compound 1 was estimated at ca. 21.8 kcal.mol(-1) exothermic.

[C(4)H(3)N(CH(2)NMe(2))-2]AlMe(2) (1) is prepared in 88% yield by the reaction of substituted pyrrole [C(4)H(4)N(CH(2)NMe(2))-2] with 1 equiv of AlMe(3) in methylene chloride. Reaction of compound 1 with 1 equiv of phenyl isocyanate in toluene generates a seven-membered cycloaluminum compound [C(4)H(3)N[CH(2)NPh(CONMe(2))]-2] AlMe(2) (2). The phenyl isocyanate was inserted into the aluminum and dimethylamino nitrogen bond and induced an unusual rearrangement which results in C-N bond breaking and formation. A control experiment shows that the reaction of substituted pyrrole [C(4)H(4)N(CH(2)NMe(2))-2] with 1 equiv of phenyl isocyanate in diethyl ether yields a pyrrolyl attached urea derivative [C(4)H(3)N(CH(2)NMe(2))-2-[C(=O)NHPh]-1] (3). The demethanation reaction of AlMe(3) with 1 equiv of 3 in methylene chloride at 0 degrees C afforded O-bounded and N-bounded aluminum dimethyl compounds [C(4)H(3)N(CH(2)NMe(2))-2-[C(=O)NPh]-1]AlMe(2) (4a) and [C(4)H(3)N(CH(2)NMe(2))-2-[CO(=NPh)]-1]AlMe(2) (4b) in a total 78% yield after recrystallization. Both 4a and 4b are observed in (1)H NMR spectra; however, the relative ratio of 4a and 4b depends on the solvent used. Two equivalents of AlMe(3) was reacted with 3 in methylene chloride to yield a dinuclear aluminum compound AlMe(3)[C(4)H(3)N(CH(2)NMe(2))-2-[C(=O)NPh]-1] AlMe(2) (5). Reaction of 5 with another equivalent of ligand 3 results in the re-formation of compounds 4a and 4b.

A series of aluminum complexes featuring with the ketiminate ligand, OCMeCHCMeNHAr (Ar = 2,6-(i)Pr(2)C(6)H(3), 1), have been prepared and characterized spectroscopically and structurally. Reactions of 1 with trialkylaluminum in 1:1 or 1:2 molar ratio generate four- and five-coordinated aluminum complexes (OCMeCHCMeNAr)AlR(2) (R = Me (2); R = Et (3)) and (OCMeCHCMeNAr)(2)AlR (R = Me (4); R = Et (5)) in high yields. Similarly, reaction of AlCl(3) with 1 or 2 equiv of the lithiated 1 in toluene afforded bis(ketiminate) aluminum chloride complex, (OCMeCHCMeNAr)(2)AlCl (6) or (OCMeCHCMeNAr)AlCl(2) (7). Surprisingly, reacting 6 with 1 equiv of AgBF(4) in methylene/acetonitrile mix-solvents generates (OCMeCHCMeNAr)(2)AlF (8) in moderate yield. The structures of complexes 2-6 and 8 have been determined by X-ray crystallography. Complexes 2 and 3 both exhibit tetrahedron structures with the aluminum atom surrounded by oxygen and nitrogen atoms of chelating ketiminate and two alkyl groups. The mono- and bis-ketiminate aluminum complexes 2-5 have shown moderate activity toward the ring-opening polymerization of epsilon-caprolactone.

Hydrocarbon solutions of Mo(2)(NMe(2))(6) and 2,2'-methylenebis(6-tert-butyl-4-methylphenol) (>/=2 equiv), HO&ndblwave;CH(2)&ndblwave;OH, yield Mo(2)(NMe(2))(2)(O&ndblwave;CH(2)&ndblwave;O)(2), I, which exists in bridged Ib and chelated Ic isomers. These are formed under kinetic control, and recrystallization allows the separation of Ib (orange cubes) from Ic (yellow cubes) both of which have been crystallographically characterized. In each there is an ethane-like O(2)NMo&tbd1;MoO(2)N core with Mo-Mo = 2.2 Å (average). In Ib the two O&ndblwave;CH(2)&ndblwave;O ligands span the Mo&tbd1;Mo bond yielding a molecule of C(2) symmetry. In Ic the molecule has near-C(2) symmetry in the solid state, but in solution there is either rapid rotation about the M&tbd1;M bond or the anti-rotamer is preferred. In benzene-d(6), Ib and Ic do not interconvert at 110 degrees C over a period of days. However, the addition of pyridine or acetonitrile causes the isomerization of Ib to Ic, thereby establishing that Ic is the thermodynamic isomer. The rate of conversion of Ib to Ic has been shown to be dependent on the square of the concentration of added pyridine: k(obs) = k[py](2). From the temperature dependence of k(obs), we determine DeltaH() = 19 (+/-1) kcal/mol and DeltaS() = -25 (+/-3) eu for the pyridine-promoted isomerization of Ib to Ic. The related reaction involving W(2)(NMe(2))(6) and HO&ndblwave;CH(2)&ndblwave;OH (>/=2 equiv) in hydrocarbon solvents at room temperature and below yields a dark brown crystalline compound, wherein C-H activation has occurred at one of the O&ndblwave;CH(2)&ndblwave;O diolate ligands, W(2)(&mgr;-H)(&mgr;-NMe(2))(NMe(2))(eta(2)-O&ndblwave;CH(2)&ndblwave;O)(eta(3)-O&ndblwave;CH&ndblwave;O)(HNMe(2)), 2. The W-W distance in 2 is 2.495(1) Å, consistent with a (W=W)(8+) core. Heating 2 in the solid-state under a dynamic vacuum leads to the elimination of HNMe(2) and the formation of 3, W(2)(NMe(2))(2)(eta(2)-O&ndblwave;CH(2)&ndblwave;O)(2), an analog of Ic. In benzene-d(6) the equilibrium involving 2 and 3 + HNMe(2) has been observed by (1)H NMR spectroscopy. The addition of pyridine to hydrocarbon solutions of 3 yields W(2)(&mgr;-H)(&mgr;-NMe(2))(eta(2)-O&ndblwave;CH(2)&ndblwave;O)(&mgr;(3)-O&ndblwave;CH&ndblwave;O)(NMe(2))(py), 4, which has been shown by single-crystal X-ray crystallography to be an analogue of 2. Studies of the addition of PMe(3) to toluene-d(8) solutions of 3 at low temperatures reveal that adduct formation occurs prior to C-H oxidative addition. For the equilibrium involving 4 and 3 + py in benzene-d(6), DeltaH degrees = 14 (+/-1) kcal/mol and DeltaS degrees = 22 (+/-3) eu.