Syntheses, Characterizations, and Coordination Chemistry of the 10-Vertex Phosphadicarbaboranes 6-R-arachno-6,8,9-PC₂B₇H₁₁ and 6-R-arachno-6,5,7-PC₂B₇H₁₁

Abstract

The 10-vertex phosphadicarbaboranes, 6-R-arachno-6,8,9-PC(2)B(7)H(11) (1) (R = Ph 1a or Me 1b) and 6-R-arachno-6,5,7-PC(2)B(7)H(11) (2) (R = Ph 2a or Me 2b) have been synthesized using in situ dehydrohalogenation reactions of RPCl(2) (R = Ph or Me) with the arachno-4,5-C(2)B(7)H(13) and arachno-4,6-C(2)B(7)H(13) carboranes, respectively. X-ray crystallographic determinations in conjunction with DFT/GIAO/NMR calculations and NMR spectroscopic studies have established that both 1 and 2 have open cage structures based on an icosahedron missing two vertexes. The two isomeric compounds differ in the positions of the carbons and bridging hydrogens on the open face. Studies of the reactions of 2a with BH(3).THF, S(8), and hydrogen peroxide demonstrated that 2a shows strong donor properties yielding the compounds endo-6-H(3)B-exo-6-Ph-arachno-6,5,7-PC(2)B(7)H(11) (3), endo-6-S-exo-6-Ph-arachno-6,5,7-PC(2)B(7)H(11) (4), and endo-6-O-exo-6-Ph-arachno-6,5,7-PC(2)B(7)H(11) (5) in which the BH(3), S, and O substitutents are bonded to an electron lone pair localized at the phosphorus endo-position. The reaction of 2a with an excess of S(8) results in the loss of a framework boron to produce the unique open-cage compound micro(7,8)-[HS(Ph)P]-hypho-7,8-C(2)B(6)H(11) (6). 2a also formed the donor complexes cis-(eta(1)-[6-Ph-arachno-6,5,7-PC(2)B(7)H(11)])(2)PtBr(2) (7) and trans-(eta(1)-[6-Ph-arachno-6,5,7-PC(2)B(7)H(11)])(2)PdBr(2) (8) in which the metal fragment is bonded in an eta(1)-fashion at the phosphorus endo-position. In these complexes, 2a is functioning as a two-electron sigma donor to the metals and can thus be considered as an analogue of the PR(3) ligands in the classical cis-(PPh(3))(2)PtBr(2) and trans-(PPh(3))(2)PdBr(2) coordination complexes. Although 1a did not show the donor properties exhibited by 2a, its dianion 6-Ph-6,8,9-PC(2)B(7)H(9)(2)(-) (1a(2)()(-)()) readily formed eta(4)-coordinated complexes with late transition metals including 8-Ph-7-(Ph(3)P)(2)-nido-7,8,10,11-PtPC(2)B(7)H(9) (9), 7-Ph-11-(eta(5)-C(5)H(5))-nido-11,7,9,10-CoPC(2)B(7)H(9) (10), and commo-Ni-(7-Ni-8'-Ph-nido-8',10',11'-PC(2)B(7)H(9))(7-Ni-8-Ph-nido-8,10,11-PC(2)B(7)H(9)) (11).

Synthesis, Characterization, and Computational Studies of 6-(RR′N)-nido-5,7-C2B8H11: A Polyborane Cluster with a Cage-Boron Having an Exopolyhedral Dative Boron−Nitrogen Double Bond

“…The fact that the bridging hydrogens in 4 and 5 adopt these edges, gives strong support to Paetzold’s proposed hybrid nido / arachno structural formulation arising from the increased cage skeletal electron count resulting from the electron-pair donation of the amino group. From this point of view, 2 and 3 could likewise be considered to have an arachno rather than nido electron count framework, but in their case, like in the arachno -6-R-6,5,7-C 3 B 7 H 11 tricarbaboranes and the arachno -6-R-6,5,7-PC 2 B 7 H 11 phosphacarboranes, the 5 and 7 cage vertices are occupied by carbons, so the bridge hydrogens are prevented from occupying the analogous C5−B10 and C7−B8 edges in these structures.…”

4 Boron

“…The coordination chemistry of these new cluster compounds with Pt(II) fragments has also been reported. 52 Carboranyl C-glycosides have been prepared. These clusters are highly watersoluble and display only a very low cytotoxicity which makes them promising candidates for use in boron neutron capture therapy for the treatment of cancer.…”