Heterometallic boride clusters: synthesis and characterization of butterfly and square pyramidal boride clusters

A number of heterometallic boride clusters have been synthesized and structurally characterized using various spectroscopic and crystallographic analyses. Thermolysis of [Ru-3(CO)(12)] with [Cp*WH3(B4H8)] (1) yielded [{Cp* W(CO)(2)}(2)(mu(4)-B){Ru(CO)(3)}(2)(mu-H)] (2), [{Cp*W(CO)(2)}(2) (mu(5) -B){Ru(CO)(3)}(2){Ru(CO)(2)}(mu-H)] (3), [{Cp*W(CO)(2)}(mu(5)-B){Ru(CO)(3)}(4)] (4) and a ditungstaborane cluster [(Cp*W)(2)B4H8Ru(CO)(3)] (5) (Cp*=eta(5)-C5Me5). Compound 2 contains 62 cluster valence-electrons, in which the boron atom occupies the semi-interstitial position of a M-4-butterfly core, composed of two tungsten and two ruthenium atoms. Compounds 3 and 4 can be described as hetero-metallic boride clusters that contain 74-cluster valence electrons (cve), in which the boron atom is at the basal position of the M-5-square pyramidal geometry. Cluster 5 is analogous to known [(Cp*W)(2)B5H9] where one of the BH vertices has been replaced by isolobal {Ru(CO)(3)} fragment. Computational studies with density functional theory (DFT) methods at the B3LYP level have been used to analyze the bonding of the synthesized molecules. The optimized geometries and computed B-11 NMR chemical shifts satisfactorily corroborate with the experimental data. All the compounds have been characterized by mass spectrometry, IR, H-1, B-11 and C-13 NMR spectroscopy, and the structural architectures were unequivocally established by crystallographic analyses of clusters 2-5.