Novel copper(I) complexes containing 1,1′-bis (diphenylphosphino) ferrocene (dppf) as a chelate and bridging ligand:: Synthesis of tetrabridged dicopper(I) complexes [Cu2(μ-η1-C≡R)2(μ-dppf)2] and x-ray crystal structure of [Cu2(μ-η1-C≡CC6H4CH3-4)2(μ-dppf)2]

Binuclear copper(I) complexes [Cu(kappa(2)-P,P-dppf)(CH3CN)(2)][BF4] (1), [Cu(kappa(2)-P,P-dppf)(bipy)][BF4] (2) containing the chelating dppf ligand (dppf = 1,1'-bis(diphenylphosphino)ferrocene) have been prepared by substitution reactions of the acetonitrile ligands from the complexes [Cu(CH3CN)(4)][BF4] and (1) with dppf and bipy, respectively. Similarly, the treatment of the complex [Cu-2(mu-dppm)(2)(CH3CN)(2)][BF4](2) with dppf in CH2Cl2 at room temperature gives the tetranuclear complex [Cu-2(mu-dppm)(2)(kappa(2)-P,P-dPPf)(2)][BF4](2) (3) The analogous bridging chloride tetranuclear complex [Cu-2(mu-Cl)(2)(kappa(2)-P,P-dppf)(2)] (4) has been also prepared by the addition of dppf to a solution in THF containing an equimolar mixture of CuCl and tetramethylethylenediamine. Complex 4 has been used as a precursor for mu-eta(1)-alkynyl bridging dicopper(I) complexes containing the framework [Cu-2(mu-dppf)(2)]. Complexes [Cu-2(mu-eta(1)-C=CR)2(mu-dppf)(2)] (R = C6H4CH3-4 (5), C6H5 (6), CH2OCH3 (7), CH2CH2CH3 (8), (eta(5)-C5H4)Fe(eta(5)-C5H5) (9)) are obtained by the treatment of complex 4 with an excess of LiC=CR in TNF. Complexes 5-9 can also be prepared from the reaction of an equimolar mixture of [Cu(C=CR)](n) and dppf in toluene at room temperature. The crystal structure of complex 5 has been determined by X-ray diffraction. The crystallographic asymmetric unit consists of three molecules of 5, all with related stereochemistries at their centers. The complex consists of two copper atoms linked by two bridging dppf ligands and two bridging alkynyl groups in a mu-eta(1) bonding arrangement with an almost planar [Cu-2(mu-eta(1)-C=CR)(2)] framework. The arylethynyl groups are nearly linear (C=C-C angles 174(2)-175(2)degrees), and the C=C distances (1.20(2)-1.21(2) Angstrom) are typical for cases of metal-acetylide sigma-bonding. Both bridging dppf ligands are twisted from the eclipsed conformation (mean value 77(2)degrees) and also show a relatively large value of the angle (mean value 56.8(6)degrees) formed by the projection of the Cp ... Cp axis of dppf onto the Cu ... Cu axis. This seems to indicate that the molecular core [Cu-2(mu-eta(1)-C=CC6H4CH3-4)(2)] is a sterically demanding system that forces the dppf ligand to adopt a relatively strained conformation.