Characterization and Reactivity of an Unprecedented Unsaturated Zero-Valent Ruthenium Species: Isolable, Yet Highly Reactive

Magnesium reduction of cis,cis,trans- RuCl 2 (CO) 2 L 2 (L = P t Bu 2 Me) yields isolable Ru(CO) 2 L 2, shown by solution spectroscopies and X-ray diffraction to have trans phosphines but cis carbonyls, in a nonplanar structure which resembles a trigonal bipyramid with one equatorial ligand missing. This unusual geometric structure is traced by ab initio (MP2) study to enhanced back-donation to CO by zero-valent Ru. This molecule reacts in time of mixing to add CO, MeNC, O 2, CS 2, C 2 H 4, or PhC⋮CPh. Rapid oxidative addition occurs with H 2, HCl, Cl 2, and PhC⋮CH. Oxidative addition is slower with MeCl, Me 3 SiH, and MeOH, which leads to more complicated reaction schemes. Reaction with PPh 2 H gives not oxidative addition but addition and displacement, yielding Ru(CO) 2 (PPh 2 H) 2 (P t Bu 2 Me) and equimolar free P t Bu 2 Me. Magnesium reduction of cis,cis,trans- RuCl 2 (CO) 2 L‘ 2 proceeds analogously for L‘ = P i Pr 3, but for L‘ = PPh 3, decomposition and ligand scavenging give Ru(CO) 2 (PPh 3 ) 3 . Reduction of cis,trans- RuCl 2 (CO)(CNMe)L 2 gives the product of oxidative addition of a t Bu C−H bond: RuH(CO)(CNMe)[η 2 -P(CMe 2 CH 2 ) t BuMe]L, showing the influence of electron density at unsaturated Ru(0) on its persistence.