Reactions of 1,4- and 2,3-Diazadienes with Titanocene and Zirconocene Complexes of Bis(trimethylsilyl)acetylene:  Acetylene Coupling or Substitution Including Subsequent C−H Activation, C−C Coupling, and N−N Cleavage to Heterobimetallic Complexes

The reaction of 1,4-diazadienes RNCHCHNR with the titanocene and zirconocene complexes of bis(trimethylsilyl)acetylene Cp₂M(L)(η²-Me₃SiC₂SiMe₃) (M = Ti, without L (1); M = Zr, L = THF (2), pyridine (3)) is a general and new method to obtain 1-metalla-2,5-diazacyclopent-3-ene complexes Cp₂M(η²-1:4-RNCHCHNR) (M = Zr, R = 2,6-ⁱPr₂C₆H₃ (4a), 4-Me-C₆H₄ (4b), Cy (4c); M = Ti, R = 2,6-ⁱPr₂C₆H₃ (5a), 4-Me-C₆H₄ (5b), Cy (5c)). In the analogous reaction with differently substituted azines RR‘CNNCRR‘ the products depend strongly on the metals used, Zr and Ti, as well as on the substituents R and R‘. With R = R‘ = Me and M = Ti, a substitution of the alkyne by the azine and a subsequent CH activation to the 1-titana-2,3-diazacyclopent-3-ene species 6 was observed. Using R = Ph and R‘ = H the acetylene was also substituted and, by a reductive coupling of two azine molecules, the paramagnetic binuclear Ti(III) complex (Cp₂Ti)₂[μ-(η⁴-2:3,6:7-PhHCNNCHPhCHPhNNCHPh) (7) was formed. With M = Zr and R = Ph and R‘ = H no substitution of the acetylene was observed, but one of the CN double bonds of the azine inserts into the Zr−C bond of the zirconacyclopropene moiety of the starting acetylene complex to yield the 1-zircona-2-azacyclopent-4-ene species 8, which is additionally stabilized by N-coordination of the second imino group as a substituent in α position to the metal. Using R = R‘ = Ph, the central N−N single bond of the azine is cleaved by both of the metals and the bis(imido) complexes Cp₂M(−NCPh₂)₂ (M = Zr (9), Ti (10)) were isolated. The central C−C bond of 7 is cleaved in a subsequent reaction with CpCo(C₂H₄)₂ and, after an activation of the N−N bond of the azine, the heterobimetallic complex (Cp₂Ti)(μ-NCHPh)₂(CpCo) (11) was formed. In the reaction of benzaldehyde azine with CpCo(C₂H₄)₂ the isoelectronic homobimetallic bis(alkylideneamido) complex (CpCo)(μ-NCHPh)₂(CpCo) (12) was prepared. In reactions of 9 and 10 with CpCo(C₂H₄)₂ heterobimetallic complexes of this type analogous to complex 11 were not obtained. All new complexes have been characterized by spectroscopic methods, and additionally, 4a, 7, 8, 10, 11, and 12 were characterized by single-crystal X-ray structure analysis.