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

Degradation of white phosphorus (P4) in the coordination sphere of transition metals is commonly divided into two major pathways depending on the Px ligands obtained. Consecutive metal-assisted P–P bond cleavage of four bonds of the P4 tetrahedron leads to complexes featuring two P2 ligands (symmetric cleavage) or one P3 and one P1 ligand (asymmetric cleavage). A systematic investigation of the degradation of white phosphorus P4 to coordinated μ,η2:2-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(iPr2Im)­(η2-C2H4)], 1 (Cp* = η5-C5Me5, iPr2Im = 1,3-di-isopropylimidazolin-2-ylidene), reacts with P4 to give [Cp*Co­(iPr2Im)­(η2-P4)], 2, the insertion product of [Cp*Co­(iPr2Im)] into one of the P–P bonds. Addition of a further equivalent of the CoI complex [Cp*Co­(iPr2Im)­(η2-C2H4)], 1, induces cleavage of a second P–P bond to yield the dinuclear complex [{Cp*Co­(iPr2Im)}2(μ,η2:2-P4)], 3, in which a kinked cyclo-P44– ligand bridges two cobalt atoms. Consecutive dissociation of the N-heterocyclic carbene with concomitant rearrangement of the cyclo-P4 ligand and P–P dissociation leads to complexes [Cp*Co­(μ,η4:2-P4)­Co­(iPr2Im)­Cp*], 4, featuring a P4 chain, and [{Cp*Co­(μ,η2:2-P2)}2], 5, in which two isolated P22– 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.