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

Abstract
NaOPh converts equimolar RuHClL2(CCHR) (L = PPr3 i 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 RuCl2−n(OPh)nL2(CHPh), alkoxides OBut 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.

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