A unique bidentate phosphane/borane ligand is present in 2, which is formed by treatment of the rhodathiaborane 1 with BH3⋅THF [Eq. (1)]. Compound 1 was prepared by the reaction of the unsaturated cluster [8,8‐(PPh3)2‐nido‐8,7‐RhSB9H10] with bis(diphenylphosphanyl)methane (dppm). The dppm–BH3 ligand in 2 coordinates to the Rh center through a P atom and a BH3 moiety, the latter by two bridging B‐H‐Rh bonds.

Reactions of the unsaturated cluster [8,8-(PPh3)2-nido-8,7-RhSB9H10] (1) with the bidentate 1,n-bis(diphenylphosphino)alkanes (CH2) n (PPh2)2, where n = 1−3 (abbreviated as dppm, dppe, and dppp, respectively), have been studied. When a 1:1 molar ratio of phosphine to rhodathiaborane is used, for dppe and dppp, simple substitution to form [8,8-(η2-dppe)-nido-8,7-RhSB9H10] (2) or [8,8-(η2-dppp)-nido-8,7-RhSB9H10] (3) is observed. However, in the presence of an excess of dppe or dppp, mixtures of the species 2 and [8,8-(η2-dppe)-9-(η1-dppe)-nido-8,7-RhSB9H10] (4) or of 3 and [8,8-(η2-dppp)-9-(η1-dppp)-nido-8,7-RhSB9H10] (5) are formed, respectively. Under both sets of conditions, when dppm is used, only one product, [8,8-(η2-dppm)-8-(η1-dppm)-nido-8,7-RhSB9H10] (6), is observed. This latter species has two dppm ligands coordinating to the metal, one in a unidentate mode and the other bidentate. Species 2 and 3 are formally unsaturated, two electrons short of the number required for the observed 11-vertex nido structure. In contrast, 4 and 5 are saturated with the cage-bonded unidentate ligand providing an additional skeletal electron pair to the cluster. The species 4 and 5 are unstable in solution; depending on the conditions, they dissociate to give free phosphine and the chelate 2 or 3 or they undergo nido to closo transformation with loss of dihydrogen, affording the corresponding 11-vertex closo compounds [1,1-(η2-dppe)-3-(η1-dppe)-closo-1,2-RhSB9H8] (17) and the dppp analogue [1,1-(η2-dppp)-3-(η1-dppp)-closo-1,2-RhSB9H8] (18). Further reaction in the case of 5 allows isolation of the linked cluster system [{1,1-(η2-dppp)-closo-1,2-RhSB9H8}2-3,3‘-(μ-dppp)] (19). The species have been characterized by NMR and mass spectrometry, and crystal structure determinations are described for 3, the OEt derivative of 3, [8,8-(η2-dppp)-9-(OEt)-nido-RhSB9H9] (14), 6, and the phosphine oxide of 17, [1,1-(η2-dppe)-3-(η1-dppeO)-closo-1,2-RhSB9H8] (20).

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Formation of metallaheteroboranes by insertion of heteroatoms into an existing metallaborane cluster, rather than adding the metal moiety to the heteroborane which is normally the case, has been achieved in the cases of carbon, nitrogen, and sulfur to produce nine-, ten-, and eleven-vertex metallaheteroborane clusters. Thus passage of acetylene through refluxing p-xylene solutions of either arachno-[(PMe3)2(CO)HIrB8H12] (1a) or nido-[(PMe3)2(CO)IrB8H11] (2a) afforded the 11-vertex cluster nido-[9,9,9-(PMe3)2(CO)-9,7,8-IrC2B8H11] (5a) in up to 44% yield. With the cage substituted species arachno-[(PMe3)2(CO)HIrB8H11Cl] (1b), the analogous product is nido-[5-Cl-9,9,9-(PMe3)2(CO)-9,7,8-IrC2B8H10] (5b) and the position of the Cl substituent in the product suggests that the acetylene moiety attacks across the open face of the intermediate nido-iridanonaborane species and that cage rearrangement does not occur during the course of the reaction. Similarly, reaction of 1a with H2S under identical conditions results in the formation nido-[2,2,2-(PMe3)2H-2,6-IrSB8H10] (9a), closo-[2,2,2-(PMe3)2H-2,1-IrSB8H8] (10), and nido-[(PMe3)2HIrS2B8H8] (11a) in overall yields of 13%, 7%, and 20%, respectively. Additionally, refluxing a solution of 1a and anhydrous hydrazine in xylene afforded a 10% yield of the novel iridaazanonaborane nido-[2,2,2-(PMe3)3-2,9-IrNB7H9] (12). The compound is the first metallaazanonaborane cluster to be described, and its formation indicates that methods similar to those used to generate azaboranes may be used on metallaboranes to generate metallazaboranes. In addition to characterization by a combination of 1H, 31P, and 11B NMR and IR spectroscopy and high-resolution mass spectrometry, single-crystal X-ray diffraction studies were carried out on compounds 5a, 9a, 10, and 12.

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Single-crystal conventional-tube and synchrotron X-ray diffraction studies of the anions in [NMe(4)][arachno-B(9)H(12)-4,8-Br(2)] 1 and K[arachno-B(9)H(14)] 2, and also of the series of adducts [arachno-B(9)H(13)-4-L], where L is P(CCH)(3) (3), NHEt(2) (4), NC(5)H(5) (5), or NH(2)CH(2)Ph (6), are reported. Structural studies of 1-6, determined at low temperatures, located all atoms, including bridging and endo-terminal hydrogen atoms. The basic boron-hydride clusters of these, and of all the other known species with the arachno nine-vertex i-nonanborane geometry reported in the literature, are isostructural and feature three bridging and two endo-terminal hydrogen atoms on the open face. This arrangement is different from that previously reported for Cs[arachno-B(9)H(14)] 7 and for [arachno-B(9)H(13)-4-(NCMe)] 9. However, a new X-ray diffraction data set and refinement experimentally confirm the [3 x mu-H, 2 x endo] arrangement for 9 also. The experimental results for 1-6 support recently reported calculations for [B(9)H(14)](-), which predict both the structures and the (11)B NMR chemical shifts. These conclusions are also supported by calculations for 3, 4, and 9 and also for the [arachno-B(9)H(13)-4-(NCS)](-) anion in [NMe(4)][B(9)H(13)(NCS)] 8.

The two clusters [8,8-(eta(2)-dppm)-8-(eta(1)-dppm)-nido-8,7-RhSB(9)H(10)] (1) and [9,9-(eta(2)-dppm)-9-(eta(1)-dppm)-nido-9,7,8-RhC(2)B(8)H(11)] (2) (dppm = PPh(2)CH(2)PPh(2)), both of which contain pendant PPh(2) groups, react with BH(3).thf to afford the species [8,8-eta(2)-(eta(2)-(BH(3)).dppm)-nido-8,7-RhSB(9)H(10)] (3) and [9,9-eta(2)-(eta(2)-(BH(3)).dppm))-nido-9,7,8-RhC(2)B(8)H(11)] (4), respectively. These two species are very similar in that they both contain the bidentate ligand [(BH(3)).dppm], which coordinates to the Rh center via a PPh(2) group and also via a eta(2)-BH(3) group. Thus, the B atom in the BH(3) group is four-coordinate, bonded to Rh by two bridging hydrogen atoms, to a terminal H atom, and to a PPh(2) group. At room temperature, the BH(3) group is fluxional; the two bridging H atoms and the terminal H atom are equivalent on the NMR time scale. The motion is arrested at low temperature with DeltaG++ = ca. 37 and 42 kJ mol(-1), respectively, for 3 and 4. Both species are characterized completely by NMR and mass spectral measurements as well as by elemental analysis and single-crystal structure determinations.

arachno-[(CO)(PMe3)2HIrB8H12] (1) reacts with HC⋮C−C(CH3)CH2 in xylene at 138 °C to afford [7-{C(CH3)CH2}-9,9,9-(CO)(PMe3)2-nido-9,7,8-IrC2B8H10] (2; 10%) together with traces of [5,5,5-(CO)(PMe3)2-μ-6,7-{CHC(CH3)CH2}-nido-5,6-IrCB8H11] (3, <1%). Compound 2 is a conventional nido 11-vertex metallacarborane with the {C2Ir} three-atom string in the open face of the cluster, whereas compound 3 is based on a nido 10-vertex {5,6-IrCB8} skeleton with C(2) of the original butyne bridging adjacent B(7) and C(6) cluster open-face positions. Compounds 2 and 3 are characterized by 1H, 31P, and 11B NMR spectroscopy and by single-crystal X-ray diffraction analysis.