Synthetic and Structural Studies of the Coordination Behavior of 2-Pyridylbis(diphenylphosphino)methane

The coordination chemistry of the potentially semilabile tridentate ligand 2-pyridylbis(diphenylphosphino)methane
(NPP) has been investigated. Bidentate (N, P) coordination occurs in CoCl2(NPP) (1) and [CdX(μ-X)(NPP)]2 (X
= Cl (2); OAc (3)), prepared from the corresponding metal salts, in fac-Re(CO)3Br(NPP) (4) and in Fe(CO)2(MA)(NPP) (6). The last is one of three products from the reaction of Fe(CO)4(MA) (MA = maleic anhydride)
with NPP, the other two being Fe(CO)3(NPP) (7; P, P coordinated) and the unusual cyclic ylid (5). The ligand shows tridentate coordination in Cr(CO)3(NPP) (9), RuCl2(PPh3)(NPP) (10), and possibly in PtCl2(NPP) (8). Carbon monoxide displaces one phosphorus arm of the ligand
in 10. Anhydrous NiCl2 and NPP react in the presence of methanol to give NiCl2(P(OMe)Ph2)(Ph2PCH2py) (12)
in which the NPP ligand has been cleaved. This in turn reacts with O2 to form trans-NiCl2(Ph2P(O)CH2py)2 (13).
The methine proton of NPP is transferred to the metal on reaction with Pt(C2H4)(PPh3)2 and [Ir(COD)(NPP)]BF4
to form the hydride complexes Pt(H)(PPh3)(NPP−H) (14) and [Ir(H)(NPP)(NPP−H)]BF4 (15). In 15 the intact
NPP ligand is tridentate. The structures of 1 − 7 and 12 − 15 have been determined.