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The tricarbonyl [Mn(CO)3{HC(pz′)3}][PF6] 1+[PF6]−(pz′ = 3,5-dimethylpyrazolyl) reacts with a range of P-, N- and C-donor ligands, L, in the presence of trimethylamine oxide to give [Mn(CO)2L{HC(pz′)3}]+{L = PEt33+, P(OEt)34+, P(OCH2)3CEt 5+, py 6+, MeCN 7+, CNBut8+and CNXyl 9+}. The complex [Mn(CO)2(PMe3){HC(pz′)3}]+2+is formed by reaction of 7+with PMe3. Complexes 2+and 6+were structurally characterised by X-ray diffraction methods. Reaction of 7+with half a molar equivalent of 4,4′-bipyridine gives a purple compound assumed to be the bridged dimer [{HC(pz′)3}Mn(CO)2(μ-4,4′-bipy)Mn(CO)2{HC(pz′)3}]2+102+. The relative electron donating ability of HC(pz′)3has been established by comparison with the cyclopentadienyl and tris(pyrazolyl)borate analogues. Cyclic voltammetry shows that each of the complexes undergoes an irreversible oxidation. The correlation between the average carbonyl stretching frequency and the oxidation potential for complexes of P- and C-donor ligands is coincident with the correlation observed for [Mn(CO)3−mLm(η-C5H5−nMen)]. The data for complexes of N-donor ligands, however, are not coincident due to the presence of a node (and phase change) between the metal and the N-donor in the HOMO of the complex as suggested by preliminary DFT calculations. [ABSTRACT FROM AUTHOR]

Monometallic complexes of the tetrakis(pyrazolyl)borate ligand [ML2{B(pz)4}] {M = Rh, Ir; L2= η-cod, η-nbd, (CO)2, (CO)(PPh3)} have two free pyrazolyl rings which can be coordinated to a second ML2unit to give the dimeric compounds [L2M{μ-B(pz)4}ML2]+, and to a metal halide to give heterobimetallic species [L2M{μ-B(pz)4}M′Cl2]. 1H NMR spectroscopy shows that [(η-cod)Rh{μ-B(pz)4}Rh(η-cod)]+1+, [(η-nbd)Rh{μ-B(pz)4}Rh(η-nbd)]+2+, [(η-cod)Ir{μ-B(pz)4}Ir(η-cod)]+3+and [(CO)2Rh{μ-B(pz)4}Rh(CO)2]+4+are fluxional at room temperature. Cooling a solution of [(η-cod)Rh{μ-B(pz)4}Rh(η-cod)]+1+to −90 °C slows the fluxional process, which involves inversion of the two B-(N–N)2-M six-membered rings. Attempts to synthesise the asymmetric complexes [(η-cod)Rh{μ-B(pz)4}Rh(η-nbd)]+7+, [(η-cod)Rh{μ-B(pz)4}Ir(η-cod)]+8+and [(η-cod)Rh{μ-B(pz)4}Rh(CO)2]+9+produced a mixture of [L2M{μ-B(pz)4}ML2]+, [L′2M′{μ-B(pz)4}M′L′2]+and the desired species. The heterobimetallic complexes [L2Rh{μ-B(pz)4}M′Cl2] (M′ = Co, L2= η-cod 10; M′ = Co, L2= η-nbd 11; M′ = Co, L = CO 12; M′ = Co, L2= (CO)(PPh3) 13; M′ = Zn, L2= η-cod 14; M′ = Zn, L2= η-nbd 15; M′ = Pd, L2= η-cod 16) possess square planar Rh(i) linked to square planar Pd(ii) or tetrahedral Zn(ii) and Co(ii) centres. The paramagnetic Co(ii) complexes give 1H NMR spectra with signals shifted over a range of 75 ppm. The UV-Vis spectra of 10–13show four bands, one MLCT at Rh and three d-d transitions arising from the spltting of the 4T1(P) excited state due to approximate C2vsymmetry at Co. [ABSTRACT FROM AUTHOR]

The binuclear cyclometalates [Pt 2Cl 2{2 -CMe 2C 6H 4P(C 6H 4(2- iPr)) 2} 2] ( 1a) and [Pt 2Cl 2{2 -CMe 2C 6H 3(4 -OMe)P(C 6H 3(2- iPr)(4 -OMe)) 2} 2] ( 1b) react with CHCl 2CHCl 2to give the corresponding mononuclear phosphine-alkene chelates [PtCl 2{2-CH 2CMeC 6H 4P(C 6H 4(2- iPr)) 2}] ( 2a) and [PtCl 2{2-CH 2CMeC 6H 3(4-OMe)P(C 6H 3(2- iPr)(4 -OMe)) 2}] ( 2b). The product 2acan also be formed directly from [PtCl 2(NC tBu) 2] and Lain CHCl 2CHCl 2or by addition of SO 2Cl 2to 1a. Addition of an excess of SO 2Cl 2to 1bgave [PtCl 2{2-CH 2CMeC 6H 3(4-OMe)P(C 6H 2(2- iPr)(4-OMe)(5-Cl)) 2}] ( 3b), a derivative of 2bfeaturing meta-chlorine substituents on the terminal P groups as a result of electrophilic aromatic substitution. A mechanism for the conversion of 1a, bto 2a, bis proposed involving an electrophilic alkyl C−H activation by a coordinatively unsaturated platinum(IV) species. The mechanism is supported by the isolation of the diplatinum(IV) cyclometalate [Pt 2Cl 2{2 -CH 2C 6H 3(4 -OMe)P(C 6H 3(2-Me)(4 -OMe)) 2}] as a mixture of synand antiisomers 5band 5b′. The crystal structures of 2aand 3bhave been determined. [ABSTRACT FROM AUTHOR]

The triazenide-bridged tetracarbonyls [(OC)2Rh(µ-p-MeC6H4NNNC6H4Me-p)2M(CO)2] (M = Rh or Ir) undergo oxidative addition of iodine across the dimetal centre, giving the [RhM]4+ complexes [I(OC)2Rh(µ-p-MeC6H4NNNC6H4Me-p)2M(CO)2I], structurally characterised for M = Ir. The anionic tricarbonyl iodide [I(OC)Rh(µ-p-MeC6H4NNNC6H4Me-p)2Rh(CO)2]− forms [I2(OC)Rh(µ-p-MeC6H4NNNC6H4Me-p)2Rh(CO)I]− by initial one-electron transfer whereas the analogous tricarbonyl phosphine complexes [(OC)(Ph3P)Rh(µ-p-MeC6H4NNNC6H4Me-p)2M(CO)2] (M = Rh or Ir) undergo bridge cleavage, giving mononuclear [Rh(p-MeC6H4NNNC6H4Me-p)I2(CO)(PPh3)] and dimeric [I(OC){RNNN(R)C(O)}M(µ-I)2M{C(O)N(R)NNR}(CO)I] (M = Rh or Ir, R = C6H4Me-p) in which CO has been inserted into a metal–nitrogen bond. [ABSTRACT FROM AUTHOR]

Convenient syntheses are described for the five-, six-, and seven-membered phosphacycles PhP(CH2)x-1, where x5 (La5), 6 (La6), 7 (La7), and ButP(CH2)x-1where x5 (Lb5), 6 (Lb6), 7 (Lb7). Treatment of PtCl2(cod) with La5-7gives cis-PtCl2(La5-7)2(1a5-7), whereas with Lb5-7a mixture of cis-PtCl2(Lb5-7)2(1b5-7) and trans-PtCl2(Lb5-7)2(2b5-7) is obtained. Metathesis of 1a7with NaI gives a mixture of cis-PtI2(La7)2(3a7) and trans-PtI2(La7)2(4a7). The crystal structures of 1a5, 1a6, 1a7, and 4a7have been determined. Comparison of the structures of 1a7and 4a7reveals that La7has variable steric bulk, with the crystallographically determined cone angle ranging from 137° (smaller than La5) to 172° (larger than La6), depending on the particular twist-chair seven-membered-ring conformations adopted. The complex cis-PtCl2(Lb6) (1b6) is fluxional on the NMR time scale at ambient temperatures, as a result of restricted PtP rotation. Treatment of Rh2Cl2(CO)4with La5-7or Lb5-7gives the expected trans-RhCl(CO)(La5-7)2(5a5-7) or trans-RhCl(CO)(Lb5-7)2(5b5-7), and from the COvalues, it is deduced that the donor strengths to rhodium(I) are in the order Lb5-7> La5-7and, within the Laand Lbseries, L7, L6> L5. An investigation into the kinetics of the oxidative addition of MeI to 5a5-7showed that the rate of reaction is in the order 5a5> 5a7> 5a6; i.e., the smallest ligand gives the highest rate. It is postulated that the flexible La7ligand adopts a lower bulk conformation and the order of decreasing rate is then in the order of increasing bulk. The rate of reaction of MeI with 5b5is 4 times faster than with 5a5, but oxidative addition was not observed with 5b6or 5b7, perhaps because steric congestion destabilizes the rhodium(III) product. A study of the rhodium-catalyzed hydroformylation of 1-octene is reported using ligands La5-7and Lb5-7, but no systematic trends were observed, and the results for La5-7were similar to those for the acyclic analogue PhPEt2. An anomalous but reproducible result is that the catalyst derived from Lb7shows negligible hydroformylation activity but rapid octene isomerization activity. The overall conclusion is that, with the rhodium complexes of the simple phosphacycles described here, no special effect of the rings was observed in the hydroformylation catalysis. An -substituent effect is identified as a common feature in several high-activity hydroformylation catalysts derived from phosphinanes. [ABSTRACT FROM AUTHOR]