Synthesis and structures of π-allylpalladium(II) complexes containing bis(1,2,4-triazol-5-ylidene-1-yl)borate ligands. An unusual tetrahedral palladium complex

Four air stable, neutral π-allylpalladium(II) complexes containing bis(1,2,4-triazol-5-ylidene-1-yl)borate ligands [H2B(RBTz)2Pd(π-allyl)] (R = nBu, 2a; tBu, 2b; 2,6-diisopropylphenyl, 2c; cyclohexyl, 2d) have been prepared and characterized. The molecular structures of 2c and 2d have been confirmed by single-crystal X-ray diffraction. To our surprise, the coordination geometry about the palladium atom in 2d is distorted tetrahedron, in which the allyl group is nearly perpendicular to the plane defined by the Pd and the carbene C atoms. To our knowledge, such configuration has not been reported for a four-coordinated palladium allyl complex.