REACTIONS OF 1,4-DIAZADIENE AND 2,3-DIAZADIENE 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 zir conocene complexes of bis(trimethylsilyl)acetylene Cp2M(L)(eta(2)-Me3S iC2SiMe3) (M = Ti, without L (1); M = Zr, L = THF (2), pyridine (3)) i s a general and new method to obtain 1-metalla-2,5-diazacyclopent-3-en e complexes Cp2M(eta(2)-1:4-RNCH=CHNR) (M = Zr, R = 2,6-(Pr2C6H3)-Pr-i (4a), 4-Me-C6H4 (4b), Cy (4c); M = Ti, R = 2,6-(Pr2C6H3)-Pr-i (5a), 4 -Me-C6H4 (5b), Cy (5c)). In the analogous reaction with differently su bstituted azines RR'C=NN=CRR' the products depend strongly on the meta ls 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 su bsequent CH activation to the 1-titana-2,3-diazacyclopent-3-ene specie s 6 was observed. Using R = Ph and R' = H the acetylene was also subst ituted and, by a reductive coupling of two azine molecules, the parama gnetic binuclear Ti(III) complex (Cp2Ti)(2)[mu-(eta(4)-2:3,6:7-PhHC=NN CHPhCHPhNN =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 zirconacycloprop ene moiety of the starting acetylene complex to yield the 1-zircona-2- azacyclopent-4-ene species 8, which is additionally stabilized by N-co ordination of the second imino group as a substituent in a position to the metal. Using R = R' = Ph, the central N-N single bond of the azin e 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 o f 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 compl ex (Cp2Ti)(mu-N=CHPh)(2)(CpCo) (11) was formed. In the reaction of ben zaldehyde azine with CpCo(C2H4)(2) the isoelectronic homobimetallic bi s-(alkylideneamido) complex (CpCo)(mu-N=CHPh)(2)(CpCo) (12) was prepar ed. In reactions of 9 and 10 with CpCo(C2H4)(2) heterobimetallic compl exes of this type analogous to complex 11 were not obtained. All new c omplexes have been characterized by spectroscopic methods, and additio nally, 4a, 7, 8, 10, 11, and 12 were characterized by single-crystal X -ray structure analysis.