Synthesis of (Vinylidene)‐ and (Cyclopropenyl)ruthenium Complexes Containing a Tris(pyrazolyl)borato (Tp) Ligand

A convenient high‐yield route to [Ru(C≡C−Ph)(Tp)(PPh 3 ) 2 ] [ 2 ; Tp = HB(pz) 3 , pz = pyrazolyl] has been found through the intermediacy of [RuCl 2 (Hpz) 2 (PPh 3 ) 2 ] ( 1 ). This complex is readily obtained on treatment of [RuCl 2 (PPh 3 ) 3 ] with 2 equiv. of pyrazole in boiling THF. The molecular structures of complexes 1 and 2 have been confirmed by single‐crystal X‐ray diffraction analysis. A number of new cationic vinylidene complexes [Ru{=C=C(Ph)CH 2 R}(Tp)(PPh 3 ) 2 ] + [ 3a , R = CN; 3b , R = HC=CH 2 ; 3c , R = CH=C(CH 3 ) 2 ; 3d , R = Ph; 3e , R = C(O)OMe] have been prepared by electrophilic addition of organic halides to complex 2 . The deprotonation reaction of 3a yields the cyclopropenyl complex 4a . One phosphane ligand of 4a is remarkably labile, being replaced by donor ligands L to yield diastereomeric mixtures of the cyclopropenyl complexes 5a − 5d mostly in an approximate 4:1 ratio. The cyclopropenyl rings in 4a and 5a are susceptible to ring opening by I 2 . In addition, treatment of 4a with n BuNC in the presence of MeOH results in substitution of a phosphane ligand by n BuNC followed by protonation of the three‐membered ring by MeOH. This is then followed by addition of methoxide to give the vinyl ether complex [Ru{C(OMe)=C(Ph)CH 2 CN}(Tp)(PPh 3 )( n BuNC)] ( 8a ). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)