The synthesis, structural, and theoretical characterization of heterobimetallic complexes [CH3Si{SiMe2N(4-CH3C6H4)}3M−Co(CO)3(L)] (M = Ti, Zr; L = CO, PPh3, PTol3) with unsupported metal−metal bonds between cobalt atoms and titanium or zirconium atoms is being reported. The synthesis of the dinuclear compounds was achieved by salt metathesis of the chlorotitanium and zirconium complexes and the alkalimetal carbonylates. X-ray crystal structure analyses of four of these heterobimetallic complexes established the unsupported metal−metal bonds [M = Ti, L = CO (3): 2.554(1) Å; M = Ti, L = PTol3 (4b): 2.473(4) Å; M = Zr, L = CO (5): 2.705(1) Å; M = Zr, L = PPh3 (6a): 2.617(1) Å] as well as the 3-fold molecular symmetries. Upon axial phosphine substitution, a metal−metal bond contraction of ca. 0.08 Å is observed, which also results in the quantum chemical structure optimizations performed on the model compounds [(H2N)3Ti−Co(CO)4] (3x) and [(H2N)3Ti−Co(CO)3(PH3)] (4x) using gradient-corrected and hybrid density functionals. A theoretical study of the homolytic dissociation of the metal−metal bonds focuses on the relaxation energies of the complex fragments and indicates that the geometrical constraints imposed by the tripod ligand lead to a major thermodynamic contribution to the stability of the experimentally investigated complexes. The central question of the polarity of the metal−metal bond is addressed by detailed analysis of the calculated electron charge distribution using natural population analysis (NPA), charge decomposition analysis (CDA), Bader's atoms in molecules (AIM) theory, and the electron localization function (ELF). Both the orbital-based NPA and CDA schemes and the essentially orbital-independent AIM and ELF analysis suggest a description of the Ti−Co bond as being a highly polar covalent single bond. The combination of AIM and ELF is employed for the first time to analyze metal−metal bond polarity and appears to be a powerful theoretical tool for the description of bond polarity in potentially ambiguous situations.
A direct Ag−Sn bond has been established for the first time by X-ray crystallography for the dimeric complex [MeSi{SiMe2N(p-Tol)}3SnAg]2 (4) [d(Ag−Sn) =2.6567(7) Å], which is the product of a phosphine ligand redistribution reaction of MeSi{SiMe2N(p-Tol)}3SnAg(PPh3) (2).
A novel type of tripodal amido ligand with a totally siliconbased (trisilylsilane-derived) ligand framework has been synthesized and coordinated to tetravalent titanium and zirconium. The key compound in the ligand synthesis i s the chlorosilane H3CSi(Si(CH3)zC1)3 (2) which upon condensation with a range of primary amines R-NH2 (R = aryl, alkyl) yields the amino-functionalized ligand precursors lated cage structures. H3CSi(Si(CH&NHRJ3 (3a-e). Their corresponding trilithium salts have been found to be the appropriate amide transfer reagents in the subsequent syntheses of the transition metal complexes. Single-crystal X-ray structure analyses of the trilithium triamide H3CSi(Si(CH3)zN(Li)tBu)3 (4a) and the Ti complex H3CSi(Si(CH3)zN(p-Tol))3TiBr (5b) have established their respective adamantane-and [2.2.2]bicyclooctane-rePolydentate amido ligands co-ordinated to high-valent transition metal atoms have provided the key to the stabilization of a wide range of molecular fragments and structural units at the metal which have been thought to be inherently labiler1~21. They may even effect the complete shielding of an otherwise highly reactive co-ordination Most of the work has thus far focused upon the first-row transition e l e m e n t~ [~~~,~] .However, there are everincreasing efforts to extend the use of such ligand systems to the co-ordination chemistry of the heavier transition element~ [~]. One of the keys to a successful implementation of this synthetic goal is the availability of polydentate amido ligands with "metal-binding sites" of the appropriate size. For example, the polydentate ligands in A and B[6,71 have been found to act as ideal chelating ligands for tetravalent titanium[*] (as well as complexes but to give poor results with the heavier group-4 metals. As this is probably due to a "mismatch" between the size of the binding site of the amido ligand and the ionic diameter of the central metal atom, a more open, but equally stable ligand system designed for the heavier early transition elements appeared desirable. With this aim we have extended the series to include a new class of amido tripods which for the first time contain a totally silicon-based ligand framework (Type C). The increasing bond lengths (C-C < C-Si < Si-Si) in the ligand framework on going from the carbon-based ligands (A) to the trisilylmethane-derived ligands (B) and then to the trisilylsilane-derived systems provide a straightforward way of controlling the size of the metal-binding cavity. In this paper we report the synthesis of a new class of amino-functionalized trisilylsilanes, the structural characterization of an adamantoidal lithium amide transfer reagent and the use of these new types of amido tripods in the synthesis of monofunctional titanium and zirconium amido halides. Results and Discussion A. Syntheses of the Amino-Functionalized Trisilylsilanes and their Conversion to the Corresponding Trilithium TriamidesThe amine precursors of the ligands may be conveniently obtained from the known silane H3CSi[Si(CH3)3]3 (1)[10-1...
The reaction of [MeSi{Me(2)SiN(Li)(p-tol)}(3)(Et(2)O)(2)] with SnCl(2) in a 1:1 molar ratio leads the tris(amido)stannate [MeSi{Me(2)SiN(p-tol)}(3)SnLi(Et(2)O)] (1), which further reacts with neutral [AuCl(PPh(3))] and anionic [PPN][AuCl(2)], PPN[AuRCl] (R = C(6)F(5), mes), and chlorogold(I) complexes yielding [Au(MeSi{Me(2)SiN(p-tol)}(3)Sn)(PPh(3))] (2) and [PPN][Au(MeSi{Me(2)SiN(p-tol)}(3)Sn)(2)] (3) and [Au(MeSi{Me(2)SiN(p-tol)}(3)Sn)(R)] (R = C(6)F(5), 4; R = mes, 5), respectively. The reaction of 1 with the dinuclear gold(II) derivative [Au(2)(CH(2)PPh(2)CH(2))(2)Cl(2)] in a 1:2 ratio affords [Au(2)(CH(2)PPh(2)CH(2))(2)(MeSi{Me(2)SiN(p-tol)}(3)Sn)(2)] (6). In a similar way but starting from PPN[Au(C(6)F(5))(3)Cl] and reacting with 1 in a 1:1 ratio, the Au(III) complex [PPN][Au(MeSi{Me(2)SiN(p-tol)}(3)Sn)(C(6)F(5))(3)] (7) has been obtained. X-ray crystal structure analyses were performed for compounds 2 and 6, establishing the Sn-Au bonds [d(Au-Sn) = 2.5651(13) and 2.6804(13) Å, respectively). Compound 6 has a nearly linear Sn-Au-Au-Sn array and features the first examples of tin-gold(II) bonds.
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