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.