Bis(2-pyridyl)phosphides and -arsenides of Group 13 Metals: Substituent-Separated Contact Ion Pairs
作者:Alexander Steiner、Dietmar Stalke
DOI:10.1021/om00005a045
日期:1995.5
Tris(2-pyridyl)phosphine reacts with lithium metal in THF with cleavage of a P-aryl bond and ligand coupling to give 2,2'-bipyridyl and lithium bis(2-pyridyl)phosphide. Hydrolysis of this solution leads to bis(2-pyridyl)phosphine 1. Deprotonation of 1 with n-butyllithium yields (THF)(2)Li(mu-Py)(2)P, 2, (Py = 2-pyridyl). Addition of trimethylaluminum to tris(2-pyridyl)phosphine gives the Me(3)Al(mu-Py)PPy(2) adduct complex 3, while deprotonation of 1 and elimination of methane forms Me(2)Al(mu-Py)(2)P, 4. 4 is also obtained by a transmetalation reaction of 2 with Me(2)AlCl. Lithium metal also cleaves one As-aryl bond in tris(2-pyridyl)arsine to give lithium bis(2-pyridyl)arsenide, which is directly treated with Me(2)AlCl and Me(2)GaCl, yielding Me(2)Al(mu-Py)(2)As, 5, and Me(2)Ga(mu-Py)(2)As, 6, respectively. While in 1 the hydrogen atom is located at the phosphorus atom, as indicated by IR and NMR spectroscopy, X-ray structure analyses of 2-5 prove that there is no contact between the metal center nd the central phosphorus or arsenic atoms of the ligand. The [Py(2)E](-) ligands (E = P, As) chelate the metal centers exclusively by both pyridyl nitrogen atoms, leaving the central E atom two-coordinated. The negative charge in the monoanionic [Py(2)E](-) ligands of 2-6 is largely delocalized from the central E atom td both pyridyl ring systems. The correspondence in spectroscopic data of 5 and 6 suggests the same structure type in the gallium arsenide complex 6.