Coordinational behavior of solvent-free diorganylzinc compounds: the remarkable x-ray structure of dimeric diphenylzinc

Abstract

The crystal structure of solvent-free diphenylzinc has been determined. Crystals of [Ph2Zn] are triclinic, space group P1, with unit cell dimensions a = 9.956 (1) A, b = 10.024 (2) A, c = 12.011 (2) b, a = 113.74(2)O, / 3 = 108.79 (1)O, y = 97.68 (2)O, and Z = 2. The structure refinement converged at RF = 0.042. A remarkable PhZn(p-Ph)zZnPh dimeric structure is found, in which the zinc atoms are tricoordinated. The structure confirms the ability of Zn to take part in multicenter bonding to carbon. It is unique not only in the sense that it is the first example of an arylzinc derivative but also because of the unsymmetrical orientation of the p-phenyl groups: they retain the predominant bonding relation to one zinc atom, as the association of the two monomeric PhzZn units only partially disturbs their original, linear geometry: the average Zn-C bond distances within one PhzZn unit are 1.946 (5) A (terminal) and 2.011 (5) A (bridging), whereas the bridging Zn-C bond to the second PhzZn unit is 2.403 (5) A. In the crystal packing, two dimeric residues are weakly associated by interactions (3.0-3.7 A) between the two zinc atoms of one dimer and one of the terminal phenyl groups of the other.

Structural Organozinc Chemistry

“…In a few cases structures having bridging alkyl or aryl groups between two zinc atoms, e.g. 1 9 , or zinc and a metal like lithium, e.g. 2 10 , copper 3a or gold, e.g.…”

“…Each of the lithium atoms is bonded to the α-carbon atoms of the two metallacycles, while a tetrahedral coordination geometry at lithium is reached by bidentate N−Li coordination (4) 102.4(2) 90.0(2) 98.90 (9) of the TMEDA molecule. The bridge bonding of the α-carbon atoms to zinc and lithium represents an example of electron-deficient two-electron three-centre type of bonding.…”

“…The X-ray crystal structure determination of diphenylzinc (53) reveals a unique structure 9 . It was known already that in apolar solvents like benzene and hexane Ph 2 Zn exists as discrete monomeric species 9,95 .…”

“…It was known already that in apolar solvents like benzene and hexane Ph 2 Zn exists as discrete monomeric species 9,95 . Therefore, it was to be expected that also in the solid Ph 2 Zn would have a linear monomeric structure like dialkylzincs and other diarylzinc compounds.…”

“…The structure of the diphenylzinc tetrahydrothiophene complex (93) is the only example of a diorganozinc compound in which Zn−S coordination bonds are present 149 . Like in diphenylzinc itself 9 the solid state structure of 93 consists of dimeric molecules in which two of the phenyl groups are bridging between two zinc atoms and each of the zinc atoms contains a terminal phenyl group. In addition, one tetrahydrothiophene molecule is coordinated to each zinc atom via its sulfur atom (Figure 48).…”