The Brellochs Reactions, of nido-B10H14 with aromatic aldehydes to give [6-Ar-nido-6-CB9H11]- anions in high yield, now permits excellent entries into C-aryl monocarbaborane chemistry, which is reviewed. From [6-Ar-nido-6-CB9H11]-, one-step cluster-closure, cluster-Aufbau, or cluster-dismantling reactions yield [1-Ph-closo-1-CB11H11]-, [7-Ph-nido-7-CB10H12]-, [1-Ph-closo-1-CB9H9]-, [2-Ph-closo-2-CB9H9]-, [4-closo-4-PhCB8H8]- and [6-Ph-arachno-6-CB8H13]. Second-step reactions involving these products yield [2-Ph-closo-2-CB10H10]-, [6-Ph-nido-6-CB8H11], [1-Ph-closo-1-CB7H7]- and [4-Ph-closo-4-CB8H8]-, as well as alternative routes to [1-Ph-closo-1-CB11H11]- and [1-Ph-closo-1-CB9H9]-. This readier access to this extensive suite of C-aryl monocarbaboranes permits a readier examination of their derivative chemistry. Monohalogenated and poly-halogenated species [1-Ph-closo-1-CB9H9-nXn]- and [1-Ph-closo-1-CB11H11-nXn]- have been formed as well as (SMe2)-substituted {CB11} and {CB10} systems. Coupling reactions with para-substituted [XC6H4CB11H10X]- systems give rod-like anions, and with poly-iodinated [PhCB11H5I6]- and [PhCB9H4I5]- give the globular [PhCB11H5Ar5I]- and [PhCB9H4Ar4I]- anions. Additional interesting species include [PhCB11H10CH=CHCH3]-, [PhCB11H10SMe(CH2)4OH]- and [PhCB9H8-6-OH]-. A review with 49 references.

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The compound [8,8-(PPh3)2-8,7-RhSBgHlo], (I), has a formal closo electron count but a nido structure, exhibits unusual fluxional behaviour in solution and reacts to ive both closo and nido compounds, e.g., cIos0-[2,3-(PPh~)~-3-(CI)-y-2; 3-(CI)-2-(Ph2P sH4)-2,3,1 -Rh2S gHs], (21, and nid0-[8,8-(PPh~)~-y-8;9-(S~CH)-8,7-RhSB~H~], (3); the structures of ( l ) , (2), and (3) were determined by X-ray crystallographic methods.

Reaction of the arachno-[ B,H,,] -or nido-[ BsHIZ] -anions with [ lrCl( PPh,),] at ca. 298 K gives, in addition to previously reported species, pale violet [7,7,9-( PPh,),-isonido-7-IrB,H,,] 2 in yields of ca. 2%. Single crystal X-ray diffraction analysis and multinuclear NM R spectroscopy reveal a ten-vertex {IrB,} cluster of an 'isonido' type that is based upon the closo eleven-vertex structure of [BllHl,]Z-from which a fourconnected vertex is removed to generate a four-membered open face. There are two fluxional bridging hydrogen atoms associated with the open face. Thermolysisat ca. 355 K of solutions in 1,1,2,2-tetrachIoroethane of yellow [5,7-(PPh,),-5-H-5-(o-Ph,PC6H,)-nido-5-lr~,H,,-2] 4 result in loss of hydrogen and the formation of deep purple [8-Cl-7,9-(PPh,),-7-(o-Ph,PC6H,)-ison~do-7-lrBsH6-1 01 5 (0-5%) and royal blue [7,9-(PPh,),-7-(o-Ph,P~6H,)-~son~do-7-IrB,H,-l 0 1 6 (045%). Single-crystal X-ray

111increased cage rea~tivity,~ further synthetic, structural, and theoretical results in this area23 should lead to a more fundamental understanding of heteroborane chemistry.Acknowledgment. I am grateful to Professors P. P. Power (University of California, Davis) and L. G. Sneddon (University of Pennsylvania) for communication of results prior to publication and to Professor T. B. Marder (University of Waterloo) for valuable discussions. Registry No. H(PMe,)21r(B8H,C1), 82447-28-7; H(PMe,)-(Ph2PC,H,)Ir(B9H8). 8325 1-41 -6. . (23) The preparation and characterization of IO-vertex, 20-skeletal-electron hyper-closo-(mes)Fe(B9H9), where mes = $-mesitylene, have recently been reported: Micciche, R. P.; Briguglio, J. J.; Sneddon, L. G. Inorg.Dr. Baker's note' emphasizes that there are interesting points regarding the interpretation of the electronic structures of a number of recently reported polyhedral boron-containing cluster compounds. It thereby underlines the need for continued synthetic and further definitive structural work in this area, for the definitive correlation of solid-state and solution structures, for the development of minimum-presumption molecular orbital theories to account for the molecular and proposed electronic structures, and subsequently for the development of definitive experimentation that can be used to assess directly, rather than by inference or intuition, the applicability of any suitable theoretical approaches that may be developed.A proportion of our work at Leeds is directed at the further exploration of some of these areas, particularly in non-carboncontaining metallaborane clusters, but it is by no means complete. Meanwhile we do not think it unreasonable to entertain the possibility that the metal-to-borane bonding in some of these new structural types may deviate from the assumption, implicit in simple electron-counting rules, that a metal cluster vertex contributes three orbitals with a quasi-conical symmetry to the cluster bonding s~h e m e .~-~ As a reviewer has emphasized, and we thank him for this, this idea is hardly new or heretical; Wade specifically addressed it 9 years ago in his 1976 electron-counting paper,6 and it has been repeatedly invoked since then (see, for example, refOne of these deviations is that the metal may, in simple terms, contribute four (or more) principal valence orbitals to the cluster bonding, rather than three.2-s*s-12 This possibility is not normally 7).Baker, R. T. Inorg. Chem., preceding paper in this issue, and references cited therein. Woollins, J. D. Polyhedron 1984, 3, 901-904. Elrington, M.; Greenwood, N. N.; Kennedy, J. D.; Thornton-Pett, M. J. Chem. Soc., Chem. Commun. 1984, 1398-1399. Crook, J. E.; Elrington, M.; Greenwood, N. N.; Kennedy, J. D.; Thornton-Pett, M.; Woollins, J. D. J. Chem. SOC., Dalton Trans. 1985, 2407-241 5. Fowkes, H.; Greenwood, N. N.; Kennedy, J. D.; Thornton-Pett, M. J .