Reaction of Bis(pyrazol-1-yl)methanes Modified by Organotin Groups on the Methine Carbon with W(CO)5THF to Give Novel Heterodinuclear Organometallic Complexes

A series of new bis(pyrazol-1-yl)methanes with organotin groups on the methine carbon have been synthesized by the reaction of bis(pyrazol-1-yl)methyllithium with organotin halide. Their reactions with W(CO) 5 THF have been investigated in detail, indicating that these new ligands display versatile reactivities upon treatment with W(CO) 5 THF, depending on the properties of the substituents on the tin atom. Treatment of triarylstannylbis(pyrazol-1-yl)methanes, Ar 3 SnCHPz 2 (Ar = phenyl or p -tolyl; Pz = substituted pyrazole), with W(CO) 5 THF results in the oxidative addition of the tin−carbon(sp 3 ) bond to the tungsten(0) center to yield novel metal−metal bonded complexes CHPz 2 (CO) 3 W−SnAr 3, in which four-membered metallacycles are found and bis(pyrazol-1-yl)methide acts as a tridentate monoanionic κ 3 -[N,C,N] chelating ligand. When there are alkyl substituents in the 4-position of pyrazole rings, some decarbonylation intermediates Ar 3 SnCHPz 2 W(CO) 4 can be isolated. Sequentially heating these intermediates can also result in the oxidative addition of the tin−carbon(sp 3 ) bond to the tungsten(0) center, implying that the oxidative addition reaction of the tin−carbon(sp 3 ) bond may form these decarbonylation intermediates. While the reactions of trialkylstannylbis(pyrazol-1-yl)methanes, R 3 SnCHPz 2 (R = Et or i Pr), with W(CO) 5 THF yield only the decarbonylation heterodinuclear complexes R 3 SnCHPz 2 W(CO) 4, in which bis(pyrazol-1-yl)methanes act as N,N-chelating bidentate ligands, no analogous oxidative addition products are obtained. However, treatment of phenyldi( tert -butyl)stannylbis(pyrazol-1-yl)methanes, ( t Bu) 2 PhSnCHPz 2 (Pz = 3,5-dimethylpyrazole or 3,4,5-trimethylpyrazole), with W(CO) 5 THF results in the oxidative addition of the tin−carbon(sp 2 ) bond instead of the tin−carbon(sp 3 ) bond to the tungsten(0) center to yield metal−metal bonded complexes ( t Bu) 2 SnCHPz 2 W(CO) 3 (Ph), in which a novel κ 3 -[N,Sn,N] coordination mode as well as asymmetric semibridging carbonyl between the W−Sn bond is observed. In addition, the reactions of trivinylstannylbis(pyrazol-1-yl)methanes, (CH 2 CH) 3 SnCHPz 2, with W(CO) 5 THF result in a vinyl group bonded to the tungsten center in η 2 -fashion to give a tridentate κ 3 -(π,N,N) coordination mode.