σ-Coordination of a P–H Bond at a Sterically Demanding Diruthenium Site: Tautomerization between Agostic μ-Phosphane and μ-Phosphanido Complexes via an η²-P–H Bond Cleavage

Abstract

A diruthenium μ-phosphane complex, {Cp‡Ru­(μ-H)}2(μ-η2-HP t Bu2) (2a; Cp‡ = 1,2,4-C5 t Bu3H2), which features an agostic Ru–H–P interaction at one ruthenium center, was synthesized by the reaction of Cp‡Ru­(μ-H)4RuCp‡ (1) with P t Bu2H. The agostic Ru–H–P interaction was stabilized by the bulky Cp‡ and t Bu groups. The agostic Ru–H–P interaction in 2a was unambiguously confirmed by X-ray diffraction. The rapid site exchange at the P–H and Ru–H–Ru positions indicated that the η2-P–H bond underwent oxidative addition in solution, yielding a μ-phospanido isomer, {Cp‡Ru­(μ-H)}2(H)­(μ-P t Bu2) (3a). The population of the μ-phosphanido isomer increased when the size of the substituent at the phosphorus atom was reduced, and μ-phosphanido complex 3b was exclusively obtained by the reaction of 1 with PPh3.

Metal-Catalyzed P–C Bond Formation via P–H Oxidative Addition: Fundamentals and Recent Advances

“…Substituent effects in related complexes suggested that agostic structures were preferred with small P substituents that were good donors . In another dinuclear system ( 6 ), exchange of the P–H and Ru–H positions was proposed to occur via reversible oxidative addition to give 7 …”

“…19 In another dinuclear system (6), exchange of the P−H and Ru−H positions was proposed to occur via reversible oxidative addition to give 7. 20 Agostic P−H bonds have also been observed in mononuclear complexes (Scheme 6). In Zr anion 8, a combination of X-ray crystallography and DFT calculations showed that the Zr−P−H angle was 66.7(8)°, and the IR P−H stretching vibration appeared at 2100 cm −1 , considerably reduced from 2288 cm −1 in the neutral Zr−PH 2 precursor.…”