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Experimental and computational studies on dendrimers possessing a Fe(porphyrin) catalytic core and polyether dendritic arms show that these macromolecules promote efficiently the (2+1) cycloaddition between a model alkene and diazomethane. The reaction is kinetically efficient and competitive with smaller catalysts. Lower generations of dendrimers exhibit a normal hyperbolic kinetic behaviour, whereas third- and fourth-generation dendrimers show a sigmoidal kinetic profile, compatible with cooperative effects most likely due to aggregation phenomena. This behaviour resembles that observed for Fe(porphyrin) containing biomolecules such as cytochromes and haemoglobin.

New C- ansa -zirconocene complexes containing methoxythiophenolate and mercaptophenolate ligands have been synthesized and characterized. The reaction of (HSC 6 H 4 - n -OMe) ( n = 2, 3 or 4) with [Zr{( t -Bu)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Me 2 ] ( 1 ) led to the formation of monosubstituted complexes [Zr{( t -Bu)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Me(κ,S-SC 6 H 4 - n -OMe)] ( n = 2 ( 2 ); n = 3 ( 3 )) and the disubstituted complex [Zr{( t -Bu)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}(κ,S-SC 6 H 4 -4-OMe) 2 ] ( 4 ). The complexes [Zr{(R)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}(κ,O-OC 6 H 4 -4-SH) 2 ] (R = t -Bu ( 6 ); R = CH 2 CH CH 2 ( 7 )) and [Zr(η 5 -C 5 H 4 ) 2 (OC 6 H 4 - n -SH) 2 ] ( n = 3 ( 9 ); n = 4 ( 10 )) have been synthesized using the corresponding dimethyl zirconocene and mercaptophenol. However, the reaction of [Zr{( t -Bu)HC(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] ( 11 ) with 4-mercaptophenol in the presence of NEt 3 led to the formation of the first example of a homoleptic six-coordinate mercaptophenolate complex of zirconium, namely [HNEt 3 ] 2 [Zr(κ,O-OC 6 H 4 -4-SH) 6 ] ( 12 ). Complex 12 can be obtained in higher yield by the reaction of ZrCl 4 with six equivalents of 4-mercaptophenol and NEt 3. The reaction of 12 with [Zr(η 5 -C 5 H 4 ) 2 Cl 2 ] gave the unexpected disubstituted complex [Zr(η 5 -C 5 H 4 ) 2 (OC 6 H 4 -4-SH) 2 ] ( 10 ). The molecular structures of 4 and 12 have been determined by single-crystal X-ray diffraction studies.

The allyl-substituted group 4 metal complexes [M{(R)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] [M = Ti, R = CH 2 CH CH 2 , ( 2 ); R = CH 2 C(CH 3 ) CH 2 ( 3 ); M = Zr, R = CH 2 CH CH 2 ( 4 ), R = CH 2 C(CH 3 ) CH 2 ( 5 )] have been synthesized by the reaction of allyl ansa -magnesocene derivatives and the tetrachloride salts of the corresponding transition metal. The dialkyl complexes [ M ( R ) CH ( η 5 - C 5 Me 4 ) ( η 5 - C 5 H 4 ) R 2 ′ ] [M = Ti, R = CH 2 =CHCH 2 , R′ = Me ( 6 ), R′ = CH 2 Ph ( 7 ); R = CH 2 C(CH 3 ) CH 2 , R′ = Me ( 8 ), R′ = CH 2 Ph ( 9 ); M = Zr, R = CH 2 CH CH 2 , R′ = Me ( 10 ), R′ = CH 2 Ph ( 11 ); R = CH 2 C(CH 3 ) CH 2 , R′ = Me ( 12 ), R′ = CH 2 Ph ( 13 )] have been synthesized by the reaction of the corresponding ansa -metallocene dichloride complexes 2–5 and two molar equivalents of the alkyl Grignard reagent. Compounds 2–5 reacted with H 2 under catalytic conditions (Wilkinson’s catalyst or Pd/C) to give the hydrogenation products [M{(R)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] [M = Ti and R = CH 2 CH 2 CH 3 ( 14 ) or R = CH 2 CH(CH 3 ) 2 ( 15 ); M = Zr and R = CH 2 CH 2 CH 3 ( 16 ) or R = CH 2 CH(CH 3 ) 2 ( 17 )]. The reactivity of 2–5 has also been tested in hydroboration and hydrosilylation reactions. The hydroboration reactions of 3 , 4 and 5 with 9-borabicyclo[3.3.1]nonane (9-BBN) yielded the complexes [M{(9-BBN)CH 2 CH(R)CH 2 CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] [M = Ti and R = H ( 18 ); M = Zr and R = H ( 19 ) or R = CH 3 ( 20 )]. The reaction with the silane reagents HSiMe 2 Cl gave the corresponding [M{ClMe 2 SiCH 2 CHRCH 2 CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] [M = Ti and R = H ( 21 ); M = Zr and R = H ( 22 ) or R = CH 3 ( 23 )]. The reaction of 22 with t -BuMe 2 SiOH produced a new complex [Zr{ t -BuMe 2 SiOSi(Me 2 )CH 2 CH 2 CH 2 CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] ( 24 ) through the formation of Si–O–Si bonds. On the other hand, reactivity studies of some zirconocene complexes were carried out, with the insertion reaction of phenyl isocyanate (PhNCO) into the zirconium–carbon σ-bond of [Zr{( n -Bu)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )} 2 Me 2 ] ( 25 ) giving [{( n -Bu)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )]}Zr{Me{κ 2 -O,N-OC(Me)NPh}] as a mixture of two isomers 26a–b . The reaction of [Zr{( n -Bu)(H)C(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}(CH 2 Ph) 2 ] ( 27 ) with CO also provided a mixture of two isomers [{( n -Bu)CH(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )]}Zr(CH 2 Ph){κ 2 -O,C-COCH 2 Ph}] 28a–b . The molecular structures of 4 , 11 , 16 and 17 have been determined by single-crystal X-ray diffraction studies.

The dialkyl complexes, [ Zr { R ( H ) C ( η 5 - C 5 Me 4 ) ( η 5 - C 5 H 4 ) } R 2 ′ ] (R = Pr i , R′ = Me ( 2a ), CH 2 Ph ( 3a ); R = Bu n , R′ = Me ( 2b ), CH 2 Ph ( 3b ); R = Bu t , R′ = Me ( 2c ), CH 2 Ph ( 3c ); R = Ph, R′ = Me ( 2d ), CH 2 Ph ( 3d )), have been synthesized by the reaction of the ansa -metallocene dichloride complex, [Zr{R(H)C(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}Cl 2 ] (R = Pr i ( 1a ), Bu n ( 1b ), Bu t ( 1c ), Ph ( 1d )), and two molar equivalents of the alkyl Gringard reagent. The insertion reaction of the isocyanide reagent, CNC 6 H 3 Me 2 -2,6, into the zirconium–carbon σ-bond of 2 gave the corresponding η 2 -iminoacyl derivatives, [Zr{R(H)C(η 5 -C 5 Me 4 )(η 5 -C 5 H 4 )}{η 2 -MeC NC 6 H 3 Me 2 -2,6}Me] (R = Pr i ( 4a ), Bu n ( 4b ), Bu t ( 4c ), Ph ( 4d )). The molecular structures of 1b , 1c and 3b have been determined by single-crystal X-ray diffraction studies.