Expansion of iridaborane clusters by addition of monoborane. Novel metallaboranes and mechanistic detail

Abstract

This work reports the results of a thermally driven cluster expansion of arachno-1-{eta5-C5Me5IrH2}B3H7, 1, with BH3.THF. In addition to the previously reported product, arachno-1-{eta5-C5Me5IrH}B4H9, 2, formed at lower temperatures, reaction at 100 degrees C permits the isolation of four new iridaboranes. Two products, nido-1-(eta5-C5Me5Ir)B5H9, 3, and nido-3-(eta5-C5Me5Ir)B9H13, 4, contain a single Ir atom and five and nine framework boron atoms, respectively. One, nido-3,4-(eta5-C5Me5Ir)2B8H12, 5, contains two Ir atoms and eight framework boron atoms. Their structures are predicted by the electron counting rules to be a nido-iridahexaborane, 3, nido-iridadecaborane, 4, and nido-diiridadecaborane, 5. The accuracy of these predictions in each case is established experimentally by spectroscopic characterization in solution and structure determinations in the solid state. A less stable metallaborane has been identified and the available spectroscopic and crystallographic information are consistent with the formulation nido-3,4-(eta5-C5Me5Ir)2B8H13(eta-BH2), 6, i.e., a species containing an exopolyhedral bridging BH group. These new observations, along with earlier ones on ruthenaborane cluster systems, are used to fully define a general mechanism for a cluster expansion reaction, i.e., addition of borane to form an exopolyhedral adduct followed by cage insertion.

Chemistry of group 9 dimetallaborane analogues of octaborane(12)

“…Therefore, we have tried to contrast their structural data and chemical shifts values with a set of similar cluster types of formal electron counts of 12 (Table 1). [14][15][16][17] The bridging hydrogens of 1 have not been located by X-ray diffraction studies; however, their connectivity have assertively been determined by 1 H NMR and are expected to be situated on the open face of the six-membered ring.…”

“…Mono-and di-cobaltaborane analogues of decaborane (14) have been synthesized and structurally characterized. It is exciting to see at what degree it might be likely to replace the BH units by {Cp*Co} fragment or metal carbonyl fragments ({Fe(CO) 3 } or {Co 2 (CO) 5 }) in B 10 cage and what would be the structural discrepancy from the parent molecules.…”

Synthesis, Structures and Chemistry of the Metallaboranes of Group 4–9 with M2B5 Core Having a Cross Cluster M–M Bond

“…Although, the bridging hydride ligands could not be located in the solid-state X-ray structure, their positions were fixed based on 1 In metallaborane chemistry, the mutually synergistic interactions of metal and organic ligands can generate molecules with interesting and diverse geometries. As evident in Table 2 [60] showing interesting sandwich structures mimicking their organometallic counterpart ferrocene. These molecules provided an additional bridge between metallaborane and organometallic chemistry.…”

Fine Tuning of Metallaborane Geometries: Chemistry of Metallaboranes of Early Transition Metals Derived from Metal Halides and Monoborane Reagents

“…[1] The development of metallaborane chemistry has followed a similar pathway, with new species often obtained from conditions that favor the thermodynamic product, either through thermolysis or by simple metathesis reactions between a preformed polyborane anion and transition-metal halides. [2][3][4][5] Detailed investigations of the Co, [6] Rh, [7] Ir, [8,9] Fe, [10] Ru, [11] Re, [12,13] Cr, [14,15] Mo, [10,[16][17][18] W, [10,19,20] and Ta [21][22][23] systems reported to date reveal that metal identity affects products. For example, the earlier transition metals facilitate dehydrogenation leading to highly condensed clusters, such as closo-A C H T U N G -T R E N N U N G [(Cp*M) 2 B n H n + m ], (M = Re: [13] n = 7-10, m = 0; M = W: [12] n = 7, m = 2), whereas late transition elements form stable nido-or arachno-metallaboranes, such as nido-[(Cp*Ru) 2 B 10 H 16 ] [24] or arachno-1-[(Cp*IrH)B 4 H 9 ].…”

“…For example, the earlier transition metals facilitate dehydrogenation leading to highly condensed clusters, such as closo-A C H T U N G -T R E N N U N G [(Cp*M) 2 B n H n + m ], (M = Re: [13] n = 7-10, m = 0; M = W: [12] n = 7, m = 2), whereas late transition elements form stable nido-or arachno-metallaboranes, such as nido-[(Cp*Ru) 2 B 10 H 16 ] [24] or arachno-1-[(Cp*IrH)B 4 H 9 ]. [9] Metallaboranes that incorporate early transition metals are a sparsely explored area of cluster chemistry [2][3][4]25] and the challenge is to find synthetic routes. Traditionally, the focus has been on two broad but complementary approaches, namely a) insertion or fragmentation reactions of ready-assembled borane frameworks and b) condensation reactions of monoboron precursors [LiBH 4 ·thf] or [BH 3 ·thf].…”