Syntheses, characterizations, and computational studies of heteroborane clusters

The main objectives of my research has been to explore the syntheses, characterizations, and reactivities of new phosphorus-heteroborane clusters, with a main focus on phosphadicarbaboranes, including (1) 10-vertex phosphadicarbaborane 6-R-arachno-6,7,8-PC2B7H11, 6-R-arachno-6,5,7-PC2B7H11 (R = Ph, Me) and their transition metal complexes, (2) 8-vertex endo-7-{Ph2(H)P}-8-R-hypho-7,8-C 2B6H11 (R = H, Me) carboranes, (3) 11-vertex 7,9-Ph2-nido-7,9-P2B9H 9 diphosphaborane, and (4) hydroamination of 6,9-(Me3S) 2-arachno-B10H12 with silylamines. In addition, possible mechanisms for the endo/exo-6-R- arachno-6,8-C2B7H12 isomerization were investigated using DFT computational methods. The first 10-vertex phosphadicarbaboranes, 6-R-arachno-6,8,9-PC 2B7H11 (R = Ph, Me) and 6-R-arachno-6,5,7-PC 2B7H11 (R = Ph, Me) were synthesized using in situ dehydrohalogenation reactions of RPCl2 (R = Ph or Me) with the arachno-4,5-C2B7H13 and arachno-4,6-C2B7H13, respectively. Single crystal X-ray crystallographic results established that the structures of 6-Ph-arachno-6,8,9-PC2B 7H11 and 6-Ph-arachno-6,5,7-PC2B 7H11. Reactions of 6-Ph-arachno-6,5,7-PC 2B7H11 with BH3·THF, S 8, and hydrogen peroxide demonstrated the basicity of the P6-phosphorus yielding the new arachno-substituted compounds, endo-6-H 3B-exo-6-Ph-arachno-6,5,7-PC 2B7H11, endo-6-S-exo -6-Ph-arachno-6,5,7-PC2B7H 11, and 6-O-exo-6-Ph-arachno-6,5,7-PC 2B7H11. The 6-Ph-arachno-6,5,7-PC 2B7H11 also has formed donor complexes with transition metals, yielding the complexes cis-(η1-[6-Ph- arachno-6,5,7-PC2B7H11])2PtBr 2 and trans-(η1-[6-Ph-arachno -6,5,7-PC2B7H11])2PdBr 2. The 6-Ph-arachno-6,8,9-PC2B7H 92− dianion formed η4-coordinated complexes including 8-Ph-7-(Ph3P)2-nido-7,8,10,11-PtPC 2B7H9, 7-Ph-11-(η5-C5 H5)-nido-11,7,9,10-CoPC2B 7H9, and two isomers of commo-Ni-(7-Ni-8 ′-Ph-nido-8′,10 ′,11′-PC2B7H 9)(7-Ni-8-Ph-nido8,10,11-PC2B7H 9). The new hypho-class heteroboranes endo-7-{Ph 2(H)P}-8-R-hypho-7,8-C2B6H 11 (R = H, Me) were prepared from the reactions of Na+[4-R- arachno-4,6-C2H11]− with Ph2PCl. In endo-7-{Ph2(H)P}-8-R- hypho-7,8-C2B6H11, the cage carbon that has the Ph2(H)P-substituent showed an ylide-like character. It has recently been shown that the endo-6-R- arachno-6,8-C2B7H12 (R = NCCH 2CH2, CH3) compounds isomerize upon heating to exo-6-R-arachno-6,8-C2B7H 12. Six different types of isomerization mechanisms were investigated using DFT calculations: (1) a simple rotation mechanism, (2) a mechanism involving the movement of one bridge hydrogen, (3) a mechanism involving the movement of two bridge hydrogens, (4) a mechanism involving the movement of an endo hydrogen, (5) a mechanism involving hydrogen exchange between the cage and the C6 substituent, and (6) a solvent assisted mechanism involving a hypho-class intermediate. The 11-vertex diphosphaborane, 7,9-Ph2-nido-7,9-P 2B9H9, was prepared from (Me4N)B 9H12 and PhPCl2 and its structure was determined by single crystal X-ray diffraction and NMR spectroscopic methods. The decaborane-methyl sulfide adduct 6,9-(Me3S)2- arachno-B10H12 was hydroaminated by hexamethyldisilazane (HMDS) and 1,1,3,3,5,5-hexamethylcyclotrisilazane (HMCTS) to afford the amine-substituted decaboranes, 6-(Me3Si)2N-nido-B 10H13 and 6-HMCTS-nido-B10H 13