Dinuclear [RNi(oxam)NiR] complexes (oxam = N1,N2-bis(2-pyridylmethyl)-N3 N4-bis(2,4,6-trimethylphenyl)- oxalamidinate; R = Me, Ph, C≡CH, C≡CPh):: Reactions of the methyl complex and formation of [Li(THF)]2Li2Ni2Me8 and [Li(THF)]4Ni2Me8

The reaction between 1 equiv of [{(acac)Ni}(2)(A)] and 2 equiv of LiR in THF afforded the binuclear organometallic complexes [(RNi)(2)(A)] (A: (NN2)-N-1-bis(2-pyridylmethyl)-N-3,N-4-bis-(2,4,6-trimethylphenyl)oxalamidinate; 1: R = Me; 2: R = Ph). Analogously, 3b (R = C dropC-H was formed from [{(acac)Ni}(2)(A)] and sodium acetylide. The reaction of I with phenylacetylene resulted in the formation of complex 3a (R = C dropC-Ph), accompanied by the evolution of methane. Compounds 1-3 were characterized by H-1 and (13) C NMR spectroscopy, elemental analysis, and mass spectroscopy. In addition, the molecular structures of 1 and 3b were determined by X-ray crystallography. The NMR spectra of the complexes showed very simple patterns, thus indicating that only one isomer is present in solution containing a highly symmetrical structure with planar Ni(II) centers. X-ray studies confirmed that two Ni(II) centers are connected via the oxalamidinato bridge A, which coordinates in a tridentate fashion at each Ni atom. The fourth position at the metal center is occupied by the organic groups R. Compound 1 reacts with an excess of LiMe in THF, yielding [Li(THF)](2)Li2Ni2Me8 (5). Upon recrystallization, the THF-enriched complex [Li(THF)](4)Ni2Me8 (6) was isolated. Both complexes were characterized by X-ray crystallography and H-1 (13) C NMR spectroscopy. Both 5 and 6 are highly symmetrical compounds in which each planar Ni(II) center is surrounded by four methyl groups. The Ni . . . Ni separations are relatively long (3.167(1) and 3.142(1) Angstrom, respectively), reflecting the absence of a metal-metal bond between those two metal centers. Furthermore, agostic Li-H interactions stabilize the structure in a way similar to that in the corresponding Cr(II) compound [Li-4(THF)(4)Cr2Me8], in which very short contacts have been found (Cr . . . Cr distance 1.968(2) Angstrom).