Robert Beck

Steric Control of Cyclometallation Reactions in Schiff-Base Complexes of Cobalt(I) Containing an Anchoring Diphenylphosphanyl Group

2-(Diphenylphosphanyl)alkyliminobenzaldehydes(2-Ph2PC6H4CHNR) react with [CoCH3(PMe3)4] forming five-membered metallacycles in complexes [(2-Ph2PC6H4CNR-C,P)Co(PMe3)3] [1: R = C2H5, 2: R = CH(CH3)2, 3: R = cyclo-C6H11] while the ortho-metallation pathway is selectively followed in the formation of [{2-Ph2PC6H3(CHNR)-C1,P}Co(PMe3)3] [4: R = C(CH3)3]. The presence of a four-membered cobaltocycle in the molecular structure of 4 was confirmed by X-ray analysis. Carbonylation of 2 and 3 gives the monocarbonyl derivatives [(2-Ph2PC6H4CNR-C,P)Co(CO)(PMe3)2] [5: R = CH(CH3)2, 6: R = cyclo-C6H11] while 4 undergoes ring expansion by insertion forming [{2-Ph2PC6H3(CHNR)CO-C,P}Co(CO)(PMe3)2] [7: R = C(CH3)3]. Monosubstitution occurs under 1 bar of ethene giving the π-ethene complexes [(2-Ph2PC6H4CNR-C,P)Co(C2H4)(PMe3)2] [8: R = CH(CH3)2, 9: R = cyclo-C6H11] and [{2-Ph2PC6H3(CHNR)-C1,P}Co(C2H4)(PMe3)2] [10: R = C(CH3)3]. The molecular structure of 9 shows an equatorial π-ethene ligand. Iodomethane oxidizes 2 and 3 to afford the cobalt(II) complexes [(2-Ph2PC6H4CNR-C,P)CoI(PMe3)2] [11: R = CH(CH3)2, 12: R = cyclo-C6H11] and oxidatively adds to 4 to give mer-trans-[{2-Ph2PC6H3(CHNR)-C1,P}CoI(CH3)(PMe3)2] [13: R = C(CH3)3]. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Cobalt induced tandem C-H activation/decarbonylation of various aromatic aldehydes and related benzylic alcohols forming mononuclear aryl monocarbonyl complexes.

Reactions between Co(CH(3))(PMe(3))(4) and various ortho-substituted aromatic aldehydes (Ar(R(1),R(2))CHO) and related benzylic alcohols (Ar(R(1),R(2))CH(2)OH) proceed with high selectivity to give the mono carbonyl complexes Aryl(R(1),R(2))(PMe(3))(3)Co(CO): R(1) = H, R(2) = CH(3) (1), R(1)= H, R(2) = ethyl (2), R(1) = CH(3), R(2) = CH(3) (3), R(1) = H, R(2) = NH(2) (4), R(1) = F, R(2) = F (5), R(1) = H, R(2) = CF(3) (6), and R(1) = H, R(2) = benzo (7). This tandem C-H bond activation/decarbonylation reaction provides easy and rapid access under mild conditions (-70 degrees C) to the first isolated trimethylphosphine stabilized aryl-monocarbonyl complexes of cobalt. X-ray diffraction studies were performed on ortho-amino substituted complex 4, ortho-trifluormethyl 6, and naphthyl derivative 7.

Meridional bicyclometalation with iron: a novel way of forming dianionic [C,N,C]-ligands

Bicyclometalation of aromatic substrates containing imine anchoring groups is achieved with a dimethyliron complex at -70 degrees C; azadiene systems undergo a regiospecific activation of 1,4-CH/N interchanged C-H bonds which may be aromatic or vinylic.

Synthesis of Surface-Analogue Square-Planar Tetranuclear Nickel Hydride Clusters and Bonding to μ4-NR, -O and -BH Ligands

Tetranuclear Ni complexes were synthesized with bonding to BH, NR, and O in atypical surface-like geometries. The previously reported electron-deficient cluster [( iPr3P)Ni]5H6 (1) reacts with N-methylmorpholine oxide to give [( iPr3P)Ni]4H4(μ4-O) (2), which contains O coordinated in the center of a square-plane arrangement of Ni atoms. Reaction of 1 with benzonitrile gave the square-planar tetranuclear Ni cluster [( iPr3P)Ni]4H4(μ4-NCH2Ph) (3), which contains an imido donor in a square-based-pyramidal geometry. This reaction also gives [( iPr3P)Ni(N≡CPh)]3 (4), with bridging benzonitrile ligands. Trimer 4 was independently synthesized from the reaction of Ni(COD)2, iPr3P, and PhC≡N. The addition of dihydrogen to a 1:1 mixture of [( iPr3P)2Ni]2(N2) and ( iPr3P)2NiCl2 yielded [( iPr3P)Ni]4(μ3-H)4(μ2-Cl)2 (5), with a tetrahedral Ni core, in contrast to the square-planar geometries of 2 and 3. The solid-state structure of 5 was determined using both X-ray and neutron diffraction. Reaction of 5 with LiBH4 gave [( iPr3P)Ni]4H4(μ4-BH)2] (6) via loss of LiCl and H2.

Bis(μ-di-phenyl-phosphan-yl)bis-[(tri-methyl-phosphane)cobalt(I)](Co-Co).

The title compound, [Co2{P(C6H5)2}2(C3H9P)4], was obtained by the addition of diphenylphosphane to a solution of Co(CH3)(C3H9P)4. The dinuclear complex molecule exhibits inversion symmetry with the inversion centre located between the two CoI atoms. The short Co—Co distance of 2.3670 (8) Å lies within the range of metal–metal double bonds. As a result of inversion symmetry, the four-membered Co2P2 core is rigorously planar, and the two bridging P(C6H5)2-ligands and the terminal C3H9P ligands are arranged in a pseudo-tetrahedral fashion about the CoI atom.