The diphosphine PPh 2CH 2C(Bu t)NN(Ph)PPh 2, which is of a new type, was prepared by treating methyl t-butyl ketone phenylhydrazone with two mole equivalents of LiBu n, followed by PPh 2Cl. This diphosphine was converted to the corresponding dioxide 2a and disulfide 2b. Treatment of [M(CO) 4(nbd)] (MMo, W or Cr; nbd=norbornadiene) with the diphosphine 1 gave the corresponding tetracarbonyl complexes [M(CO) 4{PPh 2CH 2C(Bu t)NN(Ph)PPh 2}] (MMo, 3a; W, 3b; Cr, 3c) in which the diphosphine acts as a bidentate ligand. The corresponding palladium ( 4a) and platinum ( 4b) chelate complexes of type [MCl 2{PPh 2CH 2(Bu t)NN(Ph)PPh2}] were prepared by treating 1 with [PdCl 2(NCPh) 2], [PtCl 2(cod)] or [PtCl 2(NCPh) 2]. [PtMe 2{PPh 2CH 2C(Bu t)NN(Ph)PPh 2}] ( 4d) was obtained from the reaction of 1 with [PtMe 2(cod)]. Methathesis of 4b with NaI gave the corresponding iodide 4c. Treatment of 4b with concentrated solution of ammonia gave the salt, [Pt(NH 3) 2{PPh 2CH 2C(Bu t) NN(Ph)PPh 2}]Cl 2 ( 4e). NMR spectral data are given and discussed in detail.