Symmetrical P4 Cleavage at Cobalt: Characterization of Intermediates on the Way from P4 to Coordinated P2 Units

Degradation of white phosphorus (P-4) in the coordination sphere of transition metals is commonly divided into two major pathways depending on the P-x ligands obtained. Consecutive metal-assisted P-P bond cleavage of four bonds of the P-4 tetrahedron leads to complexes featuring two P-2 ligands (symmetric cleavage) or one P-3 and one P, ligand (asymmetric cleavage). A systematic investigation of the degradation of white phosphorus P-4 to coordinated mu,eta(2:2)-bridging diphosphorus ligands in the coordination sphere of cobalt is presented. herein as well as isolation of each of the decisive intermediates on the reaction pathway. The olefin complex [Cp*Co((i)Pr(2)Im)(eta(2)-C2H4)], 1 (Cp* = eta(5)-C5Me5, (i)Pr(2)Im = 1,3-di-isopropylimidazolin-2-ylidene), reacts with P-4 to give [Cp*Co((i)Pr(2)Im)(eta(2)-P-4)], 2, the insertion product of [Cp*Co((i)Pr(2)Im)] into one of the P-P bonds. Addition of a further equivalent of the Co-I complex [Cp*Co((i)Pr(2)Im)(eta(2)-C2H4)], 1, induces cleavage of a second P-P bond to yield the dinudear complex [{Cp*Co((i)Pr(2)Im)}(2)(mu,eta(2:2)-P-4)], 3, in which a kinked cyclo-P-4(4-) ligand bridges two cobalt atoms. Consecutive dissociation of the N-heterocyclic carbene with concomitant rearrangement of the cyclo-P-4 ligand and P-P dissociation leads to complexes [Cp*Co(mu,eta(4:2)-P-4)Co((i)Pr(2)Im)Cp*], 4, featuring a P-4 chain, and [{Cp*Co(mu,eta(2:2)-P-2)}(2)], 5, in which two isolated P-2(2-) ligands bridge two [Cp*Co] fragments. Each of these reactions is quantitative if performed on an NMR scale, and each compound can be isolated in high yields and large quantities.