Formation of a cyclobutenylidene by cyclo-addition of an alkynyl-ruthenium complex to a cyano(alkynyl)ethene

In contrast to the usual formal [2+2]-cycloaddition reaction, (NC)2Cdouble bond; length as m-dashC{Ctriple bond; length of mdashC(SiPri3)}2, containing bulky alkynyl substituents, reacts with Ru(Ctriple bond; length of mdashCPh)(PPh3)2Cp to give the unprecedented cyclobutenylidene complex Ru{C(CN)2C[Ctriple bond; length of mdashC(SiPri3)]double bond; length as m-dashCC(SiPri3)double bond; length as m-dashCPhCdouble bond; length as m-dash}(PPh3)Cp, formed by addition of one of the Ctriple bond; length of mdashC(SiPri3) groups to the Ru–Ctriple bond; length of mdashCPh moiety and subsequent electronic reorganisation.