Unexpected Metal-Induced Isomerisms and Phosphoryl Migrations in Pt(II) and Pd(II) Complexes of the Functional Phosphine 2-(Bis(diphenylphosphino)methyl)-oxazoline

The reaction of the functional diphosphine 1 [1 = 2-(bis(diphenylphosphino)methyl-oxazoline] with [PtCl2(NCPh)2] or [PdCl2(NCPh)2], in the presence of excess NEt3, affords [Pt{(Ph2P)2C···C(···NCH2CH2O)}2] ([Pt(1−H-P,P)2], 3a) and [Pd{(Ph2P)2C···C(···NCH2CH2O)}2] ([Pd(1−H-P,P)2], 3b), respectively, in which 1−H is (oxazoline-2-yl)bis(diphenylphosphino)methanide. The reaction of 3b with 2 equiv of [AuCl(tht)] (tht = tetrahydrothiophene) afforded [Pd(1−H-P,N)2(AuCl)2] (4), as a result of the opening of the four-membered metal chelate since ligand 1−H, which was P,P-chelating in 3b, behaves as a P,N-chelate toward the Pd(II) center in 4 and coordinates to Au(I) through the other P donor. In the absence of a base, the reaction of ligand 1 with [PtCl2(NCPh)2] in MeCN or CH2Cl2 afforded the isomers [Pt{(Ph2P)2CC(OCH2CH2NH)}2]Cl2 ([Pt(1′-P,P)2]Cl2 (5), 1′ = 2-(bis(diphenylphosphino)methylene)-oxazolidine) and [Pt{(Ph2P)2CC(OCH2CH2NH)}{Ph2PCHC(OCH2CH2N(PPh2)}]Cl2 ([Pt(1′-P,P)(2′-P,P)]Cl2 (6), 2′ = (E)-3-(diphenylphosphino)-2-((diphenylphosphino)methylene)oxazolidine]. The P,P-chelating ligands in 5 result from a tautomeric shift of the C−H proton of 1 to the nitrogen atom, whereas the formation of one of the P,P-chelates in 6 involves a carbon to nitrogen phosphoryl migration. The reaction of 5 and 6 with a base occurred by deprotonation at the nitrogen to afford 3a and [Pt{(Ph2P)2C···C(···NCH2CH2O)}{Ph2PCHCOCH2CH2N(PPh2)}]Cl ([Pt(1−H-P,P)(2′-P,P)]Cl (7)], respectively. In CH2Cl2, an isomer of 3a, [Pt{Ph2P)2C···C(···NCH2CH2O)}{Ph2PC(PPh2)COCH2CH2N}] ([Pt(1−H-P,P)(1−H-P,N)] (8)), was obtained as a side product which contains ligand 1−H in two different coordination modes. Complexes 3b·4CH2Cl2, 4·CHCl3, 6·2.5CH2Cl2, and 8·CH2Cl2 have been structurally characterized by X-ray diffraction.