Ni-benzyne complexes

Benzynes are highly strained molecules, which are recognized as useful intermediates in organic synthesis.44 They can be isolated by coordination to transition metals.45 Similar to the reaction of the cyclohexyne species 66, Ni-benzyne complex such as 85 reacted with C02 to give the corresponding five-membered oxanickelacyle complex 86 (Scheme 31).46... 

Thermolysis of the tantalum-phenyl/methyl complex 114 led to the formation of the Ta-benzyne complex 115 and the elimination of CH4.58 Similar to the reaction of the Ni-benzyne complex 85, one molecule of C02 could be incorporated into the carbon-tantalum bond to form the tantalumcycle 116 as shown in Scheme 40.59... 

By far, the most commonly studied species among Ni-cycloalkynes are the complexes of benzynes or arynes. The synthesis of Ni-benzyne complexes is typified by the reaction of 6>/// 6>-dibromobenzene with Ni(cod)2/PEt3, followed by reaction of the resulting <9r/ o-halophenyl moiety with Li, as shown in Scheme 11. The 2,3-naphthalyne... 

Some [MX]+ ions enter into reactions in which the ligand X and the reacting molecule become chemically bonded. Polymerization processes have been observed involving the [MC4H4]+ ions (147). The butadiene complex ions [MC4H4]+ of Co and Ni are unreactive to ethyne but the Fe, Ru, and Rh ions react to yield benzene and the bare metal ion. The [MC4H4]+ complex ions of Os+, Ir+, and Pt+ react with ethyne to form the MC4I I4 + ions that probably correspond to the benzyne complexes previously observed for platinum (126). 

New nickel-benzyne complexes (143-147) have been prepared by reaction of o-dihaloarenes with Ni(COD)2 in the presence of a trialkylphosphine followed by reduction of the oxidative addition product with either Li or 1% Na/Hg in ether [e.g., Eq. (23)]. The oxidative addition reaction depends on the nature of substituents on the arene and fails to occur when strong electron-donating groups are present. Based on NMR and mass spectrometry (MS) data, the new complexes were formulated as monomeric. It had been... 

AUcynylphosphines have also been shown to undergo an interesting double insertion with Ni(0)-benzyne complexes. Thus, two equivalents of Ph2P-CC-R insert into the Ni-benzyne bond in (24) to form a series of novel naphthalene-based bis(phosphine) ligands coordinated to the Ni center (25,... 

Attempts to prepare benzyne complexes by the reactions of metal complexes with established benzyne precursors have been uniformly unsuccessful. In some cases, complexes derived from only partial decomposition of the precursors have been obtained (Cook and Jauhal, 1968). An earlier claim of the preparation of a nickel-benzyne complex by the reaction of Ni(CO)4 and diiodobenzene (Gowling et al, 1968) has been shown more recently to be erroneous (Bailey et al., 1971). The reactions between CgFsMgBr and several metal carbonyls have been studied briefly (Roe and Massey, 1970). In the reaction with Co2(CO)g, a complex of stoichiometry (alkyne)Co4(CO)io was obtained which underwent thermolysis to give perfluorofluorenone. 

Ni- and Pt-Cycles as intermediates in reactions of Ni(0)- and Pt(0)-complexes with benzyne or related small-ring alkynes 97CB1029. 

In view of the analogy between nickel-benzyne and nickel-carboryne complexes, we envisage that they may share chemical properties in reaction with unsaturated substrates. In fact, in situ generated ( j -C2BjoHio)Ni(PPh3)2 (1)... 

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