Heterometallic boride clusters: Synthesis and characterization of butterfly and square pyramidal boride clusters∗

Abstract

A number of heterometallic boride clusters have been synthesized and structurally characterized using various spectroscopic and crystallographic analyses. Thermolysis of [Ru3(CO)12] with [Cp∗WH3(B4H8)] (1) yielded [{Cp∗W(CO)2}2(μ4-B){Ru(CO)3}2(μ-H)] (2), [{Cp∗W(CO)2}2(μ5-B){Ru(CO)3}2{Ru(CO)2}(μ-H)] (3), [{Cp∗W(CO)2}(μ5-B){Ru(CO)3}4] (4) and a ditungstaborane cluster [(Cp∗W)2B4H8Ru(CO)3] (5) (Cp∗=η5-C5Me5). Compound 2 contains 62 cluster valence-electrons, in which the boron atom occupies the semi-interstitial position of a M4-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 M5-square pyramidal geometry. Cluster 5 is analogous to known [(Cp∗W)2B5H9] where one of the BH vertices has been replaced by isolobal {Ru(CO)3} fragment.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 11B NMR chemical shifts satisfactorily corroborate with the experimental data. All the compounds have been characterized by mass spectrometry, IR, 1H, 11B and 13C NMR spectroscopy, and the structural architectures were unequivocally established by crystallographic analyses of clusters 2-5.