R-Group reversal of isomer stability for RuH(X)L2(CCHR) s. Ru(X)L2(CCH2R): access to four-coordinate ruthenium carbenes and carbynes

Abstract

NaOPh converts equimolar RuHClL₂(CCHR) (L = PPr₃ⁱ and PCy₃) first to RuH(OPh)L₂(CCHR), but then, only for R = H, these isomerize to the more stable carbynes Ru(OPh)L₂(C–CH₃); the rate of isomerization is slowed considerably by THF. RuH(OPh)L₂(CCHR) can also be synthesized by reaction of RuCl₂L₂[CH(CH₂R)] with 2 NaOPh; again, only when R = H does the hydrido vinylidene isomerize to the carbyne. While phenoxide converts RuCl₂L₂(CHPh) to Ru(OPh)L₂(CPh), ia the observable intermediates RuCl_2−n(OPh)_nL₂(CHPh), alkoxides OBu^t and OAdamantyl cause phosphine displacement to give the four-coordinate carbenes Ru(OR)₂L(CHPh). DFT (B3PW91) calculations show these d⁶ species have a traditional cis-divacant octahedral structure with trans OR groups.