The coordination of low-valent group 13 organyls E I R [E = Al, Ga, In; R = Cp*, C(SiMe 3 ) 3 ] to transition metals has attracted increasing interest over the past decade. Complexes and cluster compounds of these new ligands with a number of transition metals have been isolated and characterised. The E I R moiety is formally isolobal with CO and PR 3 (R = alkyl, Cp*) or carbenes (R = chelating group) with varying σ-donor and π-acceptor properties depending on the organic group R

The synthesis and structural characterization of the novel homoleptic cluster complexes [Pd2(GaCp*)2(mu2-GaCp*)3] (1c), [Pd3(GaCp*)4(mu2-GaCp*)4] (2b) and [Pd3(AlCp*)2(mu2-AlCp*)2(mu3-AlCp*)2] (3) (Cp*=C5Me5) are presented. Furthermore, ligand exchange reactions of these cluster complexes are explored. In contrast to the electronically and sterically saturated complexes [M(ECp*)4] (M=Ni, Pd, Pt), the new unsaturated analogues [M(a)(ER)b] (E=Al, Ga, In) react with a variety of typical ligands (Cp*Al, CO, phosphines, isonitriles) to give new di- and tri-substituted compounds like [Pt2(GaCp*)2(mu2-AlCp*)3] (1d), [PdPt(GaCp*)(PPh3)(mu2-GaCp*)3] (4b), or [Pd3(PPh3)3(mu2-InCp*)(mu3-InCp*)2] (8). The trends of the reactivity of [M(a)(ER)b] as well as their fluxional behavior in solution has been elucidated by NMR spectroscopy, resulting in a mechanistic rationale for the ligand exchange reactions as well as the fluxional processes.

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The monomeric homoleptic Pt(0) complex [Pt(GaCp*)4] (1) has been synthesized by reaction of [Pt(COD)2] with GaCp* in hexane. The monomeric homoleptic Pd(0) complexes [Pd(GaCp*)4] (2) and [Pd{InC(SiMe3)3}4] (3) are accessible by reaction of [Pd(tmeda)(CH3)2] with GaCp* and [InC(SiMe3)3], respectively. These reactions were shown to proceed via methyl group transfer from palladium to indium or gallium, respectively. Complexes 1 and 2 can be used as building blocks for the synthesis of dinuclear cluster compounds. Thus, reaction of [Pt(COD)2] with 1 or 2 and subsequent addition of GaCp* yields [Pt2(GaCp*)2(μ2-GaCp*)3] (4a) and [PtPd(GaCp*)(μ2-GaCp*)3] (5a). Intermediates of this dimerization reactions, i.e., [Pt2(GaCp*)(μ2-GaCp*)3(η2-COD)] (4b) and [PtPd(GaCp*)(μ2-GaCp*)3(η2-COD)] (5b), were isolated and characterized by means of variable-temperature NMR spectroscopy.

The preparation of a di-o-phenylene-bridged tridentate PCP donor set is described starting with t-BOCaniline followed by a series of steps that include lithiation, quenching with Pr i 2 PCl, conversion to the phosphine sulfide, and assembling the unsaturated N-heterocyclic carbene unit. After desulfurization, the imidazolinium unit flanked by two phosphine units, represented as [(PCP)H]PF 6 is obtained. Subsequent reaction with group 10 M(0) reagents (Ni(COD) 2 , Pd(PPh 3 ) 4 , and Pt(PPh 3 ) 4 ) generates good yields of the corresponding metal hydride complexes, [(PCP)MH]PF 6 salts (where M ) Ni(II), Pd(II), and Pt(II)). Each of these species has been characterized by elemental analyses, NMR spectroscopy, and X-ray crystallography. All of the structures show that the PCP unit is twisted with respect to the square plane of the d 8 metal complex.Supporting Information Available: Crystallographic data for 3, 7a, 7b, and 7c (CIF files); experimental details for X-ray structure determinations. This information is available free of charge via the Internet at http://pubs.acs.org. OM9000764 (45) Gilbertson, S. R.; Wang, X.

Quantum mechanical calculations on the model compounds [Fe(ECH 3 ) 5 ] (E = Al, Ga, In) suggest the existence of the homoleptic, trigonal-bipyramidal d 8 metal complexes of the exotic ligands E

The reaction of 6 equivalents of GaCp*(Cp*= pentamethylcyclopentadienyl) with [{Cp*RhCl2}2] yields the complex [Cp*Rh(GaCp*)3(Cl)2] (1) exhibting a cage-like intermetallic RhGa3 center with Ga-Cl-Ga bridges. Treatment of this complex with GaCl3 gives the Lewis acid-base adduct [Cp*Rh(GaCp*)2(GaCl3)]. (2) Reaction of [{Cp*RhCl2}2] with understoichiometric amounts of E(I)Cp*(E = Al, Ga, In) leads to a variety of products strongly dependent on the molecular ratio of the reactants. Thus, the reduction of [{Cp*RhCl2}2] with one equivalent of E(I)Cp*(E = Al, Ga, In) gives the RhII dimer [{Cp*RhCl}2]. The insertion of 3 equivalents of InCp* into the Rh-Cl bonds of [{Cp*RhCl2}2] yields the salt [Cp*2Rh]+[Cp*Rh(InCp*){In2Cl4(mu2-Cp*)}]- (3), the anion exhibiting an intermetallic RhIn(3) center with an intramolecularly bridging Cp* ring. The reaction of [{Cp*RhCl}2] with Cp*Ga yields various insertion products. In trace amount the "all hydrocarbon" cluster complex [(RhCp*)2(GaCp*)3] (6) is obtained. The corresponding ethylene containing cluster complex [{RhCp(GaCp*)(C2H4)}2] (7) can be prepared by treatment of [RhCp*(CH3CN)(C2H4)] with GaCp*.

Oxidative addition of the tridentate N-heterocyclic carbene (NHC) diphosphine ligand precursor ([PCP]H)PF(6) (1) {[PCP] = o-(i)Pr(2)PC(6)H(4)(NC(3)H(4)N)o-C(6)H(4)P(i)Pr(2)} to Ni(COD)(2) results in the formation of the nickel(II) hydride complex ([PCP]NiH)PF(6) (2). This hydride undergoes a rapid reaction with ethylene to generate a nickel(0) complex in which an ethyl group has been transferred to the carbene carbon of the original NHC-diphosphine ligand. If the first intermediate is the anticipated square-planar nickel(II) ethyl species, then the formation of the product would require a process that involves a trans C-C coupling of the NHC carbon and a presumed Ni-ethyl intermediate. Deuterium-labeling studies provide evidence for migratory insertion of the added ethylene into the Ni-H bond rather than into the Ni-carbene linkage; this is based on the observed deuterium scrambling, which requires reversible beta-elimination, alkene rotation, and hydride readdition. However, density functional theory studies suggest that a key intermediate is an agostic ethyl species that has the Ni-C bond cis to the NHC unit. A possible transition state containing two cis-disposed carbon moieties was also identified. Such a process represents a new pathway for catalyst deactivation involving NHC-based metal complexes.