John D. Kennedy

Ten-vertex metallaborane chemistry. Aspects of the iridadecaborane closo→isonido→isocloso structural continuum

Reaction of the arachno-[B9H14]– or nido-[B9H12]– anions with [IrCl(PPh3)3] at ca. 298 K gives, in addition to previously reported species, pale violet [7,7,9-(PPh3)3-isonido-7-IrB9H10]2 in yields of ca. 2%. Single crystal X-ray diffraction analysis and multinuclear NMR spectroscopy reveal a ten-vertex {IrB9} cluster of an ‘isonido’ type that is based upon the closo eleven-vertex structure of [B11H11]2– from which a four-connected vertex is removed to generate a four-membered open face. There are two fluxional bridging hydrogen atoms associated with the open face. Thermolysis at ca. 355 K of solutions in 1,1,2,2-tetrachloroethane of yellow [5,7-(PPh3)2-5-H-5-(o-Ph2P[graphic omitted]]4 result in loss of hydrogen and the formation of deep purple [8-Cl-7,9-(PPh3)2-7-(o-Ph2P[graphic omitted]0]5(0–5%) and royal blue [7,9-(PPh3)2-7-(o-Ph2P[graphic omitted]0]6(0–5%). Single-crystal X-ray diffraction shows that compounds 5 and 6 also have isonido cluster structures, although 5 does not have bridging hydrogen atoms on the open face, suggesting that any extra electrons required for it to be isoelectronic with 2 and 6 may originate from the metal vertex. The structure of the crystal of compound 6 examined was found to contain ca. 25 mole % of the isostructural 3-chloro derivative 6a. The ten-vertex clusters 2, 5 and 6 are part of a structural continuum ranging from closo through isonido to isocloso. It is proposed that these isonido compounds represent intermediates in a variety of reactions involving nido to isocloso cluster oxidations and nido to nido rearrangements.

Nine-vertex polyhedral iridamonocarbaborane chemistry. Products of thermolysis of [(CO)(PPh3)2IrCB7H8] and emerging alternative cluster-geometry patterns

Thermolysis of [7-(CO)-7,7-(PPh3)2-7,1-IrCB7H8]1 at 250 °C resulted in isomerisation to give orange air-stable [7-(CO)-7-H-7,9-(PPh3)2-7,1-IrCB7H7]2 and its 6-(PPh3) isomer 3 as the major products. The compounds were characterised by NMR spectroscopy and single-crystal X-ray diffraction analysis on 1 and 3. The CH2Cl2 disolvate of 1 is monoclinic, space group P21/n, with a= 1394.33(10), b= 1276.81 (13), c= 2393.5(2) pm, β= 94.163(9)°, and Z= 4, and the structure was refined to R(Rg)= 0.0351 (0.0384) for 5991 reflections with I > 2.0σ(I). The CH2Cl2 monosolvate of 3 is triclinic, space group P, with a= 1150.39(11), b= 1177.08(13), c= 1498.3(2) pm, α= 88.192(9), β= 89.506(8), γ= 80.720(9)°, and Z= 2. and the structure was refined to R(Rg)= 0.0299(0.0311) for 5864 reflections with I > 2.0σ(I). The nine-vertex {IrCB7} cluster structures of 1 and 3 have quadrilateral open faces (B–B ca. 220 pm) and therefore ‘isonido’ geometries although of formal closo constitution. The cluster opening is briefly discussed in the context of a nine-vertex closo–isonido–isocloso structural continuum, in the context of other contemporaneously recognised structural continua in twelve-, eleven-, ten-, and eight- vertex boron cluster chemistry, and thence in the context of emerging general structural patterns that interrelate the isocloso, isonido and isoarachno cluster geometries.

Polyhedral metallacarbaborane chemistry: preparation, molecular structure, and nuclear magnetic resonance investigation of [3-(η5-C5Me5)-closo-3,1,2-MC2B9H11] (M = Rh or Ir)

Reaction between Cs[nido-7,8-C2B9H11] and [{M(η5-C5Me5)Cl2}2] (M = Rh or Ir) yielded orange-yellow, air-stable crystals of [3-(η5-C5Me5)-closo-3,1,2-RhC2B9H11] [compound (2), 34%] or [3-(η5-C5Me5)-closo-3,1,2-IrC2B9H11] [compound (3), 96%] both of which were characterized by their assigned 11B and 1H n.m.r. spectra and by single-crystal X-ray diffraction analyses. Crystals of (2) were orthorhombic, space group P212121, with a = 1 081.0(2), b = 1 278.2(1), c = 1 278.4(2) pm, and Z = 4; R = 0.0197, R′ = 0.0204 for 1 756 observed reflections [I > 2.0σ(I)]. Crystals of (3) were also orthorhombic, space group P212121, with a = 1 076.3(1), b = 1 282.9(1), c = 1 292.8(2) pm, and Z = 4; R = 0.0286, R′ = 0.0307, for 1 712 observed reflections [I > 2.0σ(I)]. The n.m.r. properties of the C2B9H11 fragments of (2) and (3) are compared with the 11B and hitherto unreported 1H n.m.r. characteristics of the corresponding fragments of [3-(η5-C5H5)-closo-3,1,2-CoC2B9H11] (4), closo-1,2-C2B10H12, nido-7,8-C2B9H13, and [nido-7,8-C2B9H12]−, in order to assess any n.m.r. shielding patterns that might reveal bonding trends. The unique endo/bridging open-face hydrogen atom in [nido-7,8-C2B9H12]− is discussed in the light of its n.m.r. properties.

Novel rhodathiaborane complexes derived from [(PPh3)2RhSB9H10]

The compound [8,8-(PPh3)2-8,7-RhSB9H10], (1), has a formal closo electron count but a nido structure, exhibits unusual fluxional behaviour in solution and reacts to give both closo and nido compounds, e.g., closo-[2,3-(PPh3)2-3-(Cl)-µ-2; 3-(Cl)-2-(Ph2P[graphic omitted]H8], (2), and nido-[8,8-(PPh3)2-µ-8;9-(S2CH)-8,7-RhSB9H9], (3); the structures of (1), (2), and (3) were determined by X-ray crystallographic methods.

An approach to megalo-boranes. Mixed and multiple cluster fusions involving iridaborane and platinaborane cluster compounds. Crystal structure determinations by conventional and synchrotron methods

Abstract Several new macropolyhedral metallaboranes have been isolated from thermolytic mixed cluster fusion reactions involving metallaboranes and molten B10H14 as solvent. Co-thermolysis of B10H14 with nine-vertex [(CO)(PMe3)2HIrB8H12] (1) engenders 18-vertex [(CO)(PMe3)2IrB17H20] (3), via double cluster fusion; this has the 18-vertex configuration of syn-B18H22, but with a metal atom in the 10-position. From the same reaction, triple cluster fusion engenders 28-vertex [(PMe3)2IrB26H24Ir(CO)(PMe3)2] (4), which structurally is based on an intimate interfusion of closed 10-vertex and 12-vertex subclusters, to generate a tetrahedral tetraboron core that also has a more open commo one-boron linkage to a nido nine-vertex {IrB8} subcluster. Compound 4 exhibits interesting consequences of cluster-crevice formation and introduces the concept of globular megalo-borane structures that have borons-only cores surrounded by boron-hydride sheaths. Examination for incipient megalo-borane globular behaviour in another system, viz. [IrCl(PPh3)3] (7) with anti-B18H22, reveals a four-atom core feature in 19-vertex [(PPh3)HIrB18H18(PPh3)] (6), which has a closo-type {IrB10} 11-vertex subcluster fused to a nido 10-vertex {B10} subcluster to generate a four-atom {IrB3} tetrahedron. Examination for mixed cluster fusion in other systems reveals the generation of [(PMe2Ph)2Pt-anti-B18H20] (8), from the co-thermolysis of [(PMe2Ph)2PtB8H12] (2) and B10H14, and examination for multiple cluster fusion reveals the formation of 30-vertex [(PMe2Ph)2(PMe2C6H4)2Pt2B28H32] (10), 29-vertex [(PMe2Ph)2PtB28H32] (11) and 27-vertex [(PMe2Ph)2PtB26H26(PMe2Ph)] (12) from the same reaction. Structurally, compound 10 is based on a 10-vertex arachno-{6,9-Pt2B8} unit linked, via one B–B two-electron two-centre bond each, to two 10-vertex nido-{B10} units; it also exhibits molecular condensation in the form of two P-phenylene ortho-cycloboronations. Compound 11 is based on the 19-vertex [(PMe2Ph)2Pt-η4-anti-B18H22] configuration with an additional 10-vertex nido-{B10H13} moiety bound to the non-platinated subcluster via one B–B two-electron two-centre bond. Compound 12 is based on two nido 11-vertex {PtB10} units joined by a single commo Pt vertex, with one of these units conjoined to an arachno eight-boron unit via a two-boron common edge and an open bridging {B–H(exo)–Pt–μ-B2} link. Thermolysis of [(PMe2Ph)2PtB8H12] (2) with the pre-formed double-cluster compound anti-B18H22 generates triple-contiguity 27-vertex [(PMe2Ph)PtB26H26(PMe2Ph)] (13) which, structurally, consists of a nido 11-vertex {PtB10} unit that is fused to a second 11-vertex nido {PtB10} unit with a triangular {PtB2} face in common, and also fused to a 10-vertex nido {B10} unit with a {B2} edge in common. The sequence 12→11→10→13→4 represents a progression of increasing intimacy of cluster fusion. Small crystals of compounds 3, 11 and 12 necessitated synchrotron X-radiation for sufficient diffraction intensity.

Two-dimensional 1H–1H COSY n.m.r. spectroscopy in polyhedral boron hydride chemistry

Two-dimensional 1H–1H COSY n.m.r. spectroscopy [with simultaneous {11B(broad band noise)} decoupling] is not subject to many of the limitations of 2D 11B–11B COSY experimentation in polyhedral boron hydride chemistry, and therefore can complement and extend it as a powerful new structural tool.

Carbaborane salts of [ZnCl(HpztBu)3]+, a host for inorganic anions (hpztbu = 5-tert-butylpyrazole)

The cations in [ZnCl(HpztBu)3]Y (Y− = [Co(C2B9H11)2]− or [1-Ph-closo-1-CB9H9]−) associate into dimers in the crystal, presenting a bowl-shaped face into which the carbaborane anions can pack. In contrast, the cations in [ZnCl(HpztBu)3][6,7,8,9,10-Br5-closo-1-CB9H5]·H2O associate with each other into a 1-D hydrogen-bonded polymer.

The first osmaboranes and a new iridatetraborane

Abstract The reactions of [Os(CO)ClH(PPh 3 ) 3 ] under mild conditions with the anions arachno -[B 3 H 8 ] − and nido -[B 5 H 8 − yield the first air-stable polyhedral osmaborane species arachno -[(HOsB 3 H 8 )(CO)(PPh 3 ) 2 ] (65%) and nido -[(OsB 5 H 9 )(CO)(PPh 3 ) 2 ] (80%) respectively. The 11 B and 1 H NMR properties of these osmaboranes are similar to those of their iridium analogues arachno -[(IrB 5 H 8 )(CO)(PPh 3 ) 2 ]. Mild thermolysis of nido -[(OsB 5 H 9 (CO)(PPh 3 ) 2 ] yields nido -[(OsB 4 H 8 )(CO)(PPh 3 ) 2 ] (40%) for which there is, as yet, no iridium analogue.

Eleven-vertex polyhedral metalladicarbaborane chemistry. Reactions of neutral nido-5,6-C2B8H12 and the [nido-6,9-C2B8H10]2− anion to give formally closo isomeric 1-(arene) and 1-(cyclopentadiene)-1,2,4- and 1,2,3-metalladicarbaundecaboranes, and some substituent chemistry. Chiral separations, and crystal and molecular structures of [5-Br-1-(η6-C6Me6)-1,2,4-RuC2B8H9] and [2-Me-1-(η5-C5Me5)-1,2,3-RhC2B8H9]

Abstract Reactions between nido -5,6-C 2 B 8 H 12 ( 1 ) and the organometallic halides [{MLCl 2 } 2 ] ( 2 ) [where {ML}={Ru(η 6 -C 6 Me 6 )} ( 2a ), {Ru(η 6 - p -MeC 6 H 4 i Pr)} ( 2b ), {Rh(η 5 -C 5 Me 5 )} ( 2c ), and {Os(η 6 - p -MeC 6 H 4 i Pr)} ( 2d )] in the presence of N , N , N ′, N ′-tetramethylnaphthalene-1,8-diamine (tmnda) in dichloromethane or chloroform have generated a series of the corresponding metalladicarbaboranes [1-L-1,2,4-MC 2 B 8 H 10 ] ( 3 , closo 11-vertex numbering system) [where {ML}={Ru(η 6 -C 6 Me 6 )} ( 3a ), {Ru(η 6 - p -MeC 6 H 4 i Pr)} ( 3b ), {Rh(η 5 -C 5 Me 5 )} ( 3c ), and {Os(η 6 - p -MeC 6 H 4 i Pr)} ( 3d )] in yields of 48–94%. The substituted species, [5-Br-1-(η 6 -C 6 Me 6 )-1,2,4-RuC 2 B 8 H 9 ] ( 5-Br-3a ) and [ 7-Br-1 -(η 6 -C 6 Me 6 )-1,2,4-RuC 2 B 8 H 9 ] ( 7-Br-3a ) have been obtained from a similar reaction involving [7-Br- nido -5,6-C 2 B 8 H 11 ] ( 7-Br-1 ) (combined yield 75%, separated by preparative HPLC). Each of the compounds 5-Br-3a and 7-Br-3a has been resolved into its enantiomers by use of chiral HPLC separation techniques. Analogous reactions between [{MLCl 2 } 2 ] ( 2 ) and the [ nido -6,9-C 2 B 8 H 10 ] 2− anion (species 4 2− ) have produced a series of the isomeric symmetrical complexes [1-L- closo -1,2,3-MC 2 B 8 H 10 ] ( 5 ) [where {ML}={Ru(η 6 -C 6 Me 6 )} ( 5a ), {Ru(η 6 - p -MeC 6 H 4 i Pr)} ( 5b ), {Rh(η 5 -C 5 Me 5 )} ( 5c ) and {Os(η 6 - p -MeC 6 H 4 i Pr)} ( 5d )]; the 2-methyl substituted compound [2-Me-1-(η 5 -C 5 Me 5 )- closo -1,2,3-RhC 2 B 8 H 9 ] ( 2-Me-5c ) has been prepared similarly using the [6-Me- nido -C 2 B 8 H 9 ] 2− anion (species 2-Me-4 2− ) as the starting dicarbaborane. All these compounds are characterised by mass spectrometry and 11 B- and 1 H-NMR spectroscopy. Single-crystal X-ray diffraction studies have been carried out on compounds 5-Br-3a and 2-Me-5c as two representative examples of the compounds in series 3 and in series 5 . The {MC 2 B 8 } clusters of compounds 3 have four-membered open faces, generating an ‘ isonido ’ geometry, whereas those of compounds 5 approximate more to the classical closo cluster geometry. Thermolyses of the {1,2,4-MC 2 B 8 } compounds 3a – 3d cleanly generate their corresponding {1,2,3-MC 2 B 8 } isomers 5a – 5d .

Structural chemistry of halogenated monocarbaboranes: the extended structures of Cs[1-HCB9H4Br5], Cs[1-HCB11H5Cl6] and Cs[1-HCB11H5Br6]

The crystal structures of the Cs+ salts of the halogenated monocarbaborane anions [closo-1-HCB9H4Br5]−, [closo-1-HCB11H5Cl6]− and [closo-1-HCB11H5Br6]− have been determined. The structures show two-dimensional extended-sheet or three-dimensional lattice structures and feature unusual distorted cuboctahedral and tetrakis hexahedral coordination geometries about Cs+. Incidental to the structural work, new convenient preparations of the precursive non-halogenated monocarbaborane anions [closo-1-HCB9H9]− and [closo-1-HCB11H11]− are presented.