Carbon-ligands

These hydrated salts contain bidentate carbonate ligands and no water molecules are bound directly to the central metal atom. The only single-crystal x-ray diffraction studies available are those for salts of (4) (52—54) and the mineral tuliokite [128706 2-3], Na2BaTh(C03)2 -6H20], which contains the unusual Th(C02) 2 anion (5) (55). 

The known uranium(VI) carbonate soHds have empirical formulas, 1102(003), M2U02(C03)2, and M4U02(C03)3. The soHd of composition 1102(003) is a well-known mineral, mtherfordine, and its stmcture has been determined from crystals of both the natural mineral and synthetic samples. Rutherfordine is a layered soHd in which the local coordination environment of the uranyl ion consists of a hexagonal bipyramidal arrangement of oxygen atoms with the uranyl units perpendicular to the orthorhombic plane. Each uranium atom forms six equatorial bonds with the oxygen atoms of four carbonate ligands, two in a bidentate manner and two in a monodentate manner. 

These mechanisms ascribe in jortance to the Lewis acid-Lewis base interaction between the allyl halide and the organolithium reagent. When substitution is complete, the halide ion is incorporated into the lifliium cluster in place of one of the carbon ligands. 

Transition Metal Complexes of Neutral Tti -Carbon Ligands... 

The differences observed in the chemistry of these dinuclear gold(I) amidinate complexes compared with dinuclear gold(I) complexes with sulfur and carbon ligands may be understood by examining their respective highest occupied molecular orbital (HOMO)s and lowest unoccupied molecular orbital (LUMO)s of the species. 

X-ray diffraction studies on [TpBut,Me]Zn 2(/i,-r)1,Tj1-C03) have identified that the bridging carbonate ligand is coordinated to each zinc center in a unidentate fashion (171,172), which thereby provides additional support for the presence of a unidentate, rather than bidentate, bicarbonate ligand in [TpBut,Me]Zn(0C02H). The carbonate complex [TpBut,Me]Zn 2(/iA-7)1,T)1-C03) is also characterized by v(CO) absorptions at 1587 and 1311 cm-1 in the IR spectrum (173), and a 13C NMR signal at 8 164 ppm (in C6D6). 

Secondly, the molecular structure of [TpPr 2]Zn 2(/u,-7)1,7)2-C03), as determined by x-ray diffraction (151,153), reveals that the carbonate ligand is coordinated in an asymmetric manner, with unidentate coordination to one zinc center and bidentate coordination to the other zinc center, i.e., fi-ri1,ri2-C03 (Scheme 24). Such coordination is noticeably distinct from that of [TpBut Me]Zn 2(/x.-r)1,7 1-C03), in which the carbonate ligand bridges in a symmetric unidentate mode. 

Thirdly, it is significant that the difference in coordination modes of the bridging carbonate ligands of [TpPrl2]Zn 2(/u.-i71,rj2-C03) and [TpBut,Me]Zn 2(jLt-7j1,T71-C03) is manifested in their reactivity. Thus, whereas [TpButMe]Zn 2(/i-T71,i71-C03) reacts instantaneously with H20... 

The ability of cobalt(II), nickel(II), and copper(II) to exhibit a greater tendency than Zn(II) towards bidentate coordination is further illustrated by structural comparisons within a series of bridging carbonate complexes (188). For example, of the complexes [TpPr 2]M 2(/x-C03) (M = Mn, Fe, Co, Ni, Cu, Zn), only the zinc derivative does not exhibit bidentate coordination at both metal centers (151,153). Furthermore, the carbonate ligand in the complexes [TpPr 2]M 2(/x-C03) (M = Mn, Fe, Co, Ni, Cu) also exhibits varying degrees of asymmetry that closely parallel the series of nitrate complexes described earlier (Fig. 47 and Table IX). 

Symmetric bis(unidentate) coordination of bridging carbonate ligands has been observed previously. See ... 

An important contribution of the resonance form b requires the donation of electron density form the metal to the dienyl ligand [M(dM) -> C(pn-) contribution], The presence of a carbonyl group (a strong TT-acceptor ligand) trans to the dienyl reduces the M(dM) - C(ptt) contribution and, therefore, the nucleo-philicity of the unsaturated ii -carbon ligand. Then the nucleophilic center of the molecule is not the alkenyl ligand but the metallic center, and the protonation at the metal leads to the olefin via reductive elimination from a hydride-dienyl intermediate.24... 

Dihalocarbene ligands, like other neutral 2-e donor carbon ligands, are expected to participate in migratory-insertion reactions when bound adjacent to a rx-bound alkyl or hydride ligand. An example is provided by the following reaction (119) ... 

The discovery of 1 (1), in 1970, opened a new and fascinating chapter of organometallic chemistry. This cation was the first compound derived from the hypothetical borabenzene 2 and the first complex of a classical boron-carbon ligand. Since then approximately 100 borabenzene derivatives, mainly complexes of 3d metals, have been characterized. Other unsaturated boron-carbon systems have been shown to act as ligands to metals (2). This development has also strongly stimulated the challenging quest for the simple species 2-5. 

The reaction of Co2(CO)8 with 25 is complicated at room temperature, but above 60°C Co(CO)2(C5H5BPh) (11) is obtained as the only complex product (29). Ni(CO)4 reacts with 25 in boiling hexane to give the (cyclopentadienyl)(cyclopentenyl)nickel analog 49 [5(nB) = 24.4 ppm, one broad signal] this complex contains a novel boron-carbon ligand with... 

---