1,4-Diaza-1,3-diene (DAD) complexes of early transition elements. Syntheses, structures and molecular dynamics of mono- and bis(eta(5)-cyclopentadienyl)titanium-, zirconium- and hafnium(DAD) complexes. Crystal- and molecularstructures of CpTi(DAD)CH2Ph, [CpTi(DAD)](2)O, CpZr[(DAD)((NO)-O-boolean AND)] and Cp2Hf(DAD)

Treatment of CpTiCl3 and CpZrCl3(THF)(2) with one equivalent magnesium in t he presence of 1,4-diaza-1,3-dienes ((RN)-N-1=(CRCR2)-C-2=NR1 (R-1,R-2-DAD; R-1 = C6H4-2-Me, C6H4-4-Me, C6H4-4-OMe, R-2 = H, Me, Ph) yields the monome ric titanium complexes CpTi(R-1,R-2-DAD)Cl (2, R-1 = C6H4-4-OMe, R-2 = H; 3 , R-1 = C6H4-2-Me, R-2 = Me; 4, R-1 = C6H4-4-OMe, R-2 = Me; 5, R-1 = C6H4-4 -Me, R-2 = Ph), and the chloro bridged dimeric zirconium complexes [CpZr(R- 1,R-2-DAD)Cl](2) (6, R-1 = C6H4-4-OMe, R-2 = H; 7, R-1 = C6H4-4-OMe, R-2 = Me; 8, R-1 = C6H4-4-Me, R-2 = Ph). Both the half-sandwich complexes of DAD ligands bearing alkyl (3, 4 and T) and aryl (5, 8) substituents at the inne r carbon atoms and the complexes without substituents at this DAD positions (2, 6) prefer the sigma (2),pi -coordination geometry with a supine confor mation of the heterodiene. Alkylation of the new half-sandwich DAD complexe s with one equivalent of PhCH2MgCl or one equivalent of MeMgI affords the b enzyl and methyl derivatives CpM(R-1,R-2-DAD)CH2Ph (9, M = Ti, R-1 = C6H4-4 -OMe, R-2 = Me; 10, M = Zr, R-1 = C6H4-4-OMe, R-2 = Me) and CpZr(R-1,R-2-DA D)Me (11, R-1 = C6H4-4-Me, R-2 = Ph). An X-ray study of the benzyl derivati ve 9 reveals that the alkylation does not change appreciably the DAD bondin g parameters in comparison with the starting chloride complex 4. The monome ric half-sandwich zirconium complex CpZr(R-1,R-2-DAD)((NO)-O-boolean AND) ( 12, R-1 = C6H4-4-OMe, R-2 = H) which has been prepared by reaction of 6 wit h the chelating acetylacetoneiminate compound Na[(C6H4-4-Me)N=C(Me)-CH=C(Me )O] (Na[(NO)-O-boolean AND]) as well as the oxygen bridged complex [CpTi(R- 1,R-2-DAD)](2)O (13, R-1 = C6H4-2-Me, R-2 = Me) which has been formed by hy drolysis of 3 also keep the supine conformation of the heterodiene ligand w ith respect to the Cp group. Temperature dependent NMR spectra of a series of different titanocene DAD complexes Cp2Ti(R-1,R-2-DAD) (R-1 = Ph, C6H4-2- Me, C6H4-4-Me, C6H4-4-OMe, 1-C10H7, R-2 = Me; 14-18) have been used to esti mate the energy barrier of the thermal induced inversion of the folded diaz ametallacyclopentene rings and to identify rotameric isomers derived from r estricted rotation of the C6H4-2-Me and the 1-C10H7 group about the N-C-ips o bond of the DAD ligand. Accordingly, complexes 16 and 18 and also the hal f-sandwich complexes 3 and 13 adopt mixtures of meso and rac rotamers. Fina lly, the crystal structure of Cp2Hf(R-1,R-2-DAD) (21, R-1 = R-2 = Ph) is re ported. (C) 2001 Elsevier Science B.V. All rights reserved.