Reaction of [RhCl(NBD)] 2 with 2.0 equiv of triphos (triphos ) bis(2-diphenylphosphinoethyl)phenylphosphine; NBD ) bicyclo[2.2.1]hepta-2,5-diene) in THF solution at room temperature affords [Rh(NBD)(triphos)][Cl] (4a), which was isolated as [Rh(NBD)(triphos)]-[SbF 6 ] (4b) in 67% yield. Treatment of 4b with aqueous formaldehyde in THF solution at 80 °C forms [Rh(CO)(triphos)][SbF 6 ] (2a), which reversibly binds a second equivalent of CO (g) to give [Rh(CO) 2 (triphos)][SbF 6 ] (2b). The complex [Rh(CO)(triphos)][SbF 6 ] has been found to be an effective aldehyde decarbonylation catalyst for primary and aryl aldehydes at temperatures as low as that of refluxing dioxane, with little or no undesirable side products resulting from β elimination or radical rearrangement.Supporting Information Available: Tables of X-ray crystallographic data for complex 4c. This material is available free of charge via the Internet at http://pubs.acs.org. OM9905106
A synthetic sequence involving the initial reaction of a substituted phosphorus dihalide (RPCl(2), R = CH(3), C(6)H(5)) with the arachno-CB(8)H(13)(-) (1-) monoanion followed by an in situ dehydrohalogenation reaction initiated by Proton Sponge, resulted in phosphorus cage insertion to yield the first 10-vertex arachno- and nido-phosphamonocarbaboranes, exo-6-R-arachno-6,7-PCB(8)H(12) (2a, 2b) and PSH(+)6-R-nido-6,9-PCB(8)H(9)(-) (PSH+3a-, PSH+3b-) (R = C(6)H(5) (a), CH(3) (b)). Alternatively, 2a and 2b were synthesized in high yield as the sole product of the reaction of the arachno-4-CB(8)H(12)(2-) (1(2-)) dianion with RPCl(2). Crystallographic determinations of PSH+3a- and PSH+3b- in conjunction with DFT/GIAO computational studies of the anions have confirmed the expected nido cage framework based on an octadecahedron missing the six-coordinate vertex. DFT/GIAO computational studies have also shown that while the gross cage geometries of the exo-6-R-arachno-6,7-PCB(8)H(12) compounds 2a and 2b resemble the known isoelectronic arachno-6,9-SCB(8)H(12), the phosphorus and carbon atoms are in thermodynamically unfavorable adjacent positions on the six-membered puckered face. They also each have an endo-hydrogen at the P6-position arising from proton transfer to the basic phosphorus during the cage-insertion reaction. Possible stepwise reaction pathways that can account for the formation of both the arachno and nido products are discussed. Deprotonation of 2a and 2b resulted in the formation of their corresponding conjugate monoanions, 6-R-arachno-6,7-PCB(8)H(11)(-) (2a-, 2b-), in which the proton that had been attached to the P6 atom was removed. Reactions of 2a- with O(2), S(8), BH(3).THF, or Br(2) further demonstrated the basicity of the P6-phosphorus yielding the new arachno-substituted compounds, endo-6-O-exo-6-(C(6)H(5))-arachno-6,7-PCB(8)H(11)(-) (4a-), endo-6-S-exo-6-(C(6)H(5))-arachno-6,7-PCB(8)H(11)(-) (5a-), endo-6-BH(3)-exo-6-(C(6)H(5))-arachno-6,7-PCB(8)H(11)(-) (6a-), and endo-6-Br-exo-6-(C(6)H(5))-arachno-6,7-PCB(8)H(11) (7a), respectively, in which the O, S, BH(3), and Br substituents are bound to the phosphorus at the endo position.
The first 10-vertex phosphadicarbaboranes, 6-R-arachno-6,8,9-PC2B7H11 1 (R = Ph 1a or Me 1b) and 6-Me-arachno-6,5,7-PC2B7H11 2 have been synthesized in good yields and structurally characterized with the aid of DFT/GIAO/NMR calculations in conjunction with multinuclear NMR studies.
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).
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