Bis(keto-phosphane) and Bis(enolato-phosphane) Ruthenium Complexes − Synthesis and X-ray Structure Determination of RuCl(NO)[η2-(P,O)-Ph2PCH=C(tBu)O]2

Abstract

A slow reaction consisting of a cleavage of one Ru−Cl bond occurred when a mixture of RuCl2[Ph2PCH2C(tBu)=O]2 (1) and [NH4][PF6] was dissolved in methanol as shown by a subsequent reaction with carbon monoxide affording the stable cationic derivative {RuCl(CO)[Ph2PCH2C(tBu)=O]2}[PF6] (2). By contrast, the straightforward reaction of 1 with carbon monoxide yielded RuCl2(CO)[Ph2PCH2C(tBu)=O][Ph2PCH2C(=O)tBu] (3) which contains unreactive Ru−Cl bonds. The isomerization of 2, which is induced under sun light exposure, is the preliminary step to the selective formation of the all‐cis bis(enolato‐phosphane) derivative (ccc)Ru(CO)2[η2‐(P,O)‐Ph2PCH=C(tBu)O]2 (9). The isomeric bis(enolato‐phosphane) derivative (cct)‐Ru(CO)2[η2‐(P,O)‐Ph2PCH=C(tBu)O]2 (10), with trans phosphorus and cis carbonyl ligands, respectively, was selectively obtained under mild basic conditions, starting from (cct)‐RuCl2(CO)2[Ph2PCH2C(=O)tBu]2 (4), which results from the reaction of 3 with carbon monoxide under thermal activation. Through an oxidative addition process, the reaction of 1 with [NO][BF4] yielded {RuCl2(NO)[Ph2PCH2C(tBu)=O][Ph2PCH2C(=O)tBu]}[BF4] (13) with trans phosphorus and trans chloride ligands, respectively. Simple deprotonation of 13 generated the enolato‐phosphane RuIV complex RuCl2(NO)[Ph2PCH=C(tBu)O][Ph2PCH2C(=O)tBu] (14) which retains the same geometry. Under basic conditions, the bis(enolato‐phosphane) derivative RuCl(NO)[η2‐(P,O)‐Ph2PCH=C(tBu)O]2 (15) was obtained. The formation of 15 surprisingly showed a trans to cis rearrangement of the two phosphorus coordinating atoms, as further confirmed by an X‐ray structure determination.