Borane reaction chemistry. Alkyne insertion reactions into boron-containing clusters. Products from the thermolysis of [6,9-(2-HC[triple bond]C-C5H4N)2-arachno-B10H12

The stirring of ortho-(HCtriple bond]C)-C(5)H(4)N] with nido-B(10)H(14)] in benzene affords 6,9-{ortho-(HCtriple bond]C)-C(5)H(4)N}(2)-arachno-B(10)H(12)] 1 in 93% yield. In the solid state, 1 has an extended complex three-dimensional structure involving intramolecular dihydrogen bonding, which accounts for its low solubility. Thermolysis of 1 gives the known 1-(ortho-C(5)H(4)N)-1,2-closo-C(2)B(10)H(11)] 2 (13%), together with new micro-5(N),6(C)-(NC(5)H(4)-ortho-CH(2))-nido-6-CB(9)H(10)] 3 (0.4%), micro-7(C),8(N)-(NC(5)H(4)-ortho-CH(2))-nido-7-CB(10)H(11)] (0.4%) , 4 binuclear endo-6'-(closo-1,2-C(2)B(10)H(10))-micro-(1(C),exo-6'(N))-(ortho-C(5)H(4)N)-micro-(exo-8'(C),exo-9'(N))-(ortho-(CH(2)CH(2))-C(5)H(4)N)-arachno-B(10)H(10)] (0.5%) 5, and exo-6(C)-endo-6(N)-(ortho-(CHdouble bond]CH)-C(5)H(4)N)-exo-9(N)-(ortho-(HCtriple bond]C)-C(5)H(4)N)-arachno-B(10)H(11)] 6. An improved solvent-free route to 2 is also presented. This set of compounds features an increasing cluster incorporation of the ethynyl moiety, initially by an effective internal hydroboration, affording an arachno to nido and then a nido to arachno:closo sequence of cluster geometry. An alternative low-temperature route to internal hydroboration is demonstrated in the room temperature reaction of closo-B(11)H(11)]N(n)Bu(4)](2) with CF(3)COOH and ortho-(HCtriple bond]C)-C(5)H(4)N], which gives micro-1(C),2(B)-ortho-C(5)H(4)N-CH(2)]-closo-1-CB(11)H(10)] 7 (40%) in which one carbon atom is incorporated into the cluster; a similar reaction with ortho-(Ntriple bond]C)-C(5)H(4)N] affords N(n)Bu(4)]7-(ortho-Ntriple bond]C-C(5)H(4)N)-nido-B(11)H(12)], 8 (68%) and stirring ortho-(Ntriple bond]C)-C(5)H(4)N] with nido-B(10)H(14)] quantitatively affords the cyano analogue of 1, 6,9-{ortho-(Ntriple bond]C)-C(5)H(4)N}(2)-arachno-B(10)H(12)] 9. All compounds were characterised by single-crystal X-ray diffraction analysis and NMR spectroscopy.