INSERTION OF TRANSITION-METALS INTO THE PHOSPHORUS-PHOSPHORUS BOND OF 1,2-DIHYDRO-1,2-DIPHOSPHETES - TOWARD THE PHOSPHORUS ANALOGS OF METAL DITHIOLENE COMPLEXES

The Insertion of NiL2 (L = phosphine) into the P-P bond of 1,2,3,4-tetraphenyl-1,2-dihydro-1,2-diphosphete has been achieved via two methods. In the first, the P-P bond is initially cleaved with lithium and the derivatized dianion allowed to react with [NiCl2L2]. This yields primarily a nickeladiphospholene with a distorted square-planar geometry at the metal in which the chelating ligand acts as a (1 + 1) electron donor, and the metal is formally in the +2 oxidation state. The second route involves the direct insertion of a [NiL2] fragment into the P-P bond at low temperature. In this case the results suggest the formation of a 1,4-diphosphadiene complex of nickel(0) in which the ligand acts as a (2 + 2) electron donor and the geometry at the metal is tetrahedral. Although both forms can be isolated for some coligands, only one form is observed in several cases and isomerization between the two forms has been observed in the other cases. The second route has also been transposed to platinum. The crystal structures of the Ni(Ph2PCH2CH2PPh2) and Pt(PPh3)2 complexes have been studied and a distortion from planarity observed in each case as shown by interplane LML/PMP angles of 38-degrees and 57-degrees, respectively. The phosphorus atoms are closer to planarity and the ring C=C bond lengths longer in the platinum complex than in the nickel. The platinum complex can be seen as lying halfway between a 1,4-diphospholene platinum(II) and a 1,4-diphosphadiene platinum(0) complex. This work suggests that with an adequate choice of coligand and substitution pattern it would be possible to achieve an electronic delocalization similar to that observed in metal-dithiolenes.