A simple and high-yield route to iridium, rhodium, osmium and ruthenium nido-6-metalladecaborane compounds

We report a high-yield heterogeneous solid/liquid phase synthetic method to a series of nido-6-metalladecaboranes. The hydridoirida- and hydridorhoda-decaboranes, [6,6,6-H(PPh₃)₂-nido-6-MB₉H₁₃] [M = Ir (1), Rh (2)] are isolatable in 98% yields from the reaction of the square-planar M(I) complexes, [MCl(PPh₃)₃] (M = Rh, Ir), with K[B₉H₁₄]. The same synthetic procedure, but using [MCl(CO)H(PPh₃)₃] (M = Ru, Os) as metal starting reagents produces the CO-ligated clusters, [6,6,6-(CO)(PPh₃)₂-nido-6-MB₉H₁₃] [M = Ru (3), Os (4)], in yields of 83% and 95%, respectively. These highly convenient syntheses permit the investigation of the reaction chemistry of the new nido-6-metalladecaboranes. Thus, the CO-ligated compounds, 3 and 4, react with the square-planar platinum(II) complex, [PtCl₂(PMe₂Ph)₂], in the presence of potassium triethylborohydride, to give the bimetallic clusters, [1,1,1-(CO)H(PPh₃)-isocloso-1-RuB₉H₈-μ-(1,2)-{Pt(PMe₂Ph)₂}] (5) and [7,7-(PMe₂Ph)₂-9,9,9-(CO)(PPh₃)₂-nido-7,9-PtOsB₉H₁₁] (6), and the monometallic nido-5-osamadecaborane, [5,5,5-(PPh₃)₂(CO)-nido-5-OsB₉H₁₃] (7). This reactivity illustrates the potential of polyhedral boron-based clusters as molecular scaffolds ("B-frames") for the construction of multimetallic species. Single-crystal X-ray diffraction analyses have revealed the molecular structures of 3, 5, 6 and 7; the compounds are also studied by multielement NMR spectroscopy, mass spectrometry, IR spectroscopy, and in some cases computationally. Futhermore, the rotation of the {M(X)(PR₃)₂} moiety (X = H, CO), as PH₃-ligated models, is studied by means of DFT-calculated relaxed potential energy surface scans, giving some insight into the lability of the metal-to-borane fragment interaction and of the exo-polyhedral ligands.

The contrarotational fluxionality of [3,3-(PMe2Ph)2-closo-3,1,2-PtC2B9H11] and related species

DFT calculations allied with experimental crystallographic and NMR results elucidate the energetics and the geometrical and (11)B nuclear shielding changes in the contrarotational fluxionality of [3,3-(PMe2Ph)2-closo-3,1,2-PtC2B9H11] and confirm the identities of two stable rotational conformers. There is a relatively unhindered contrarotation of the {Pt(PR3)2} and nido-shaped carbons-together {C2B9H11} entities about an axis that contains the platinum atom, with a transition from trihapto to tetrahapto to pentahapto metal-to-cluster interaction as the rotation progresses from 0° to 90°, and a reversal as it progresses in turn through to 180°, and thence through a similar cycle through to 360° for a complete rotation. The overall energy minimum is the trihapto conformation, but there is also an island of stability for the tetrahapto conformation at slightly higher energy, corresponding to experimental observation of these two configurations. The highest-energy pentahapto mode constitutes a transition state, and its energy defines the activation energy for the complete contrarotation, which is matched by activation energies derived from NMR spectroscopy. The shallow minima and small energy differences suggest that ready cluster flexibility will be expected about the minima, again in accord with subtle rotamer angle differences seen in experimental results. Nuclear magnetic shielding criteria suggest significant changes in intracluster bonding as the rotation progresses. The trihapto bonding geometry and the corresponding electronic structure are favoured over quite a substantial arc (some 40°) of the rotation, before rapid changes ensue, and then, after progression through the tetrahapto conformation, the electronics and the bonding geometry then again remain similar within the pentahapto mode for a further 40° or so of the rotational arc about this transition state.

Polyhedral metallaheteroborane chemistry. Synthesis, spectroscopy, structure and dynamics of eleven-vertex {RhNB9} and {PtCB9} metallaheteroboranes

Reaction between [RhCl(PPh(3))(3)] and the [nido-6-NB(9)H(11)](-) anion in CH(2)Cl(2) yields orange eleven-vertex [8,8-(PPh(3))(2)-nido-8,7-RhNB(9)H(11)]. Reaction of the [nido-6-CB(9)H(12)](-) anion with [cis-PtCl(2)(PMe(2)Ph)(2)] in methanol affords yellow eleven-vertex [9-(OMe)-8,8-(PMe(2)Ph)(2)-nido-8,7-PtCB(9)H(10)], which is also formed from the reaction of MeOH with [8,8-(PPh(3))(2)-nido-8,7-PtCB(9)H(10)]. Both compounds have been characterised by single-crystal X-ray diffraction analysis and examined by NMR spectroscopy and have structures based on eleven-vertex nido-type geometries, with the metal centre and the heteroatoms in the adjacent (8)- and (7)-positions on the pentagonal open face. The metal-to-heteroborane bonding sphere of is fluxional, with a DeltaG(double dagger) value of 48.4 kJ mol(-1). DFT calculations on the model compounds [8,8-(PH(3))(2)-nido-8,7-RhNB(9)H(11)] and [8,8-(PH(3))(2)-nido-8,7-RhSB(9)H(10)] have been carried out to define the fluxional process and the intermediates involved.

Pentahapto-bonded gold heteroborane clusters [3-(R3P)-closo-2,1-AuTeB10H10]? and [3-(R3P)-closo-3,1,2-AuAs2B9H9]?

Gold acetylide compounds [(R3P)AuC[triple bond]CC(Me)(OH)Et], where R = Ph 1 or cyclohexyl (Cy) 2, were synthesised and 2 was characterised using X-ray diffraction techniques. The solid-state structure of 2 contained a two-coordinate gold atom and a linear P-Au-C[triple bond]C-C bonding sequence. The reactions between 1 or 2 and [NR4][nido-7,8-As2B9H10] or [NR4][nido-7-TeB10H10] in ethanol-acetone solvent afforded the twelve-vertex cluster species [NMe4][3-(R3P)-closo-3,1,2-AuAs2B9H9], where R = Ph 5 or Cy 6, or [NEt4][3-(R3P)-closo-2,1-AuTeB10H10], where R = Ph 7 or Cy 8, in moderate or low yields (ca. 35% for , and and ca. 20% for ). Compounds and were characterised with X-ray crystallographic techniques. Although there was crystallographic disorder in the {As2B3} and {TeB4} rings to which the gold atoms were attached, the structures of 5 and 7 strongly suggested that the gold atoms were pentahapto bonded to all the atoms in the {As2B3} or {TeB4} rings giving formally closo cluster geometries with closo cluster electron counts. The solution-phase NMR properties of 5, 6 and 7 were consistent with closo descriptions.