3 Boron By A. J. WELCH Department of Chemistry University of Edinburgh Edinburgh EH9 3JJ 1 Introduction The plenary lectures of the Fifth International Symposium on Boron Chemistry held in Swansea in July 1983 have been published.’ Solid-phase reactions of amorphous a-,and P-B with C Si and O2 have been studied a-B having the greatest reactivity and affording boron carbide SiB4 and B60 all of which are isostructural with it2 A separate study3 compares the stabilities of a-B and B60 towards acidic and alkaline media. Ni,B3 Ni2B NiB and B70 are reported4 to be among the products obtained from the high-temperature reaction between BN and Ni. The bonding in B,,C2 has been investigated by band-structure calculations (the valence bands are flat in almost all directions in keeping with a low electrical conductivity) and by cluster cal~ulations.~ It is suggested that the carbon-rich phase BI2C3 is more stable if the icosahedra are B,,C and the intericosahedral chains C-B-C.ThB, and HfBI2have been synthesized at high pressures,6 and have been shown to be isostructural with cubic UBI2. The overall structure and metal atom distribution in y-AlB, is more complicated but recently has been reinvestigated by Higashi via single-crystal diffraction and molecular orbital (MO) calculation^.^ Higashi and Ito have also studied LiA1B14 by X-ray methods and report that the results of population analyses of the valence electrons suggest’ charge transfer from the metal atoms (Li0.7+ All.’+) to the icosahedral cage (B12)1.2- and more importantly intercage boron atoms BO.’-.The unit cell dimension of Sml-,B6 decreases linearly with increasing x within the range x = 0-0.1 but thereafter is constant indicating the existence of a two-phase regime in boron-rich samples. In contrast there is no real change in cell dimension for the lanthanum boride LaB to Lao,75B6.9 A new series of ternary ‘ Pure Appl. Chem. 1983 55 1387. ’ I. A. Bairamashvili D. Sh. Dzhobava G. I. Kalandadze Yu. I. Soloev A. M. Eristavi and G. P. Lornidze Izv. Akud. Nuuk SSSR Neorg. Muter. 1983 19 214. Ya. A. Ugai N. E. Solov’ev and V. S. Makarov Zh. Neorg. Khim. 1983 28 1334. D. M. Karpinos and S. P. Listovnichaya Izv. Akad. Nuuk SSSR Neorg. Muter. 1983 19,121I. D.R. Armstrong J. Bolland P. G. Perkins G.Will and A. Kirfel Actu Crystallogr. Sect. B 1983 39 324. J. F.Cannon and P. B. Farnsworth J. Less-Common Met. 1983 92,359. ’ I. Higashi J. Solid State Chem. 1983 47 333. * T. Ito and I. Higashi Actu Crystullogr. Sect. B 1983 39,239. Yu. B. Paderno and T. Lundstrom Actu Chem. Scund. Sect. A 1983 37,609. 19 A. J. Welch borides (MI -x Rh,y)Rh3B2 involving lanthanide elements (M) and rhodium has been synthesized and structurally and magnetically studied." All have structures based on CeCo,B,. (Mn,-,M,)B species (M = Cr or Mo) were reported last year and now the same group of workers has expanded the range to include M = Ta and M = W derivatives." Within the homogeneity ranges studied all these species have Ta,B,-type structures. The competitive synthesis of TiB2 versus Tic in a variety of Ti/C/B mixtures under a variety of experimental conditions has also been the subject of a recent study.I2 Three publications from Lucci Antonione and co-workers have appeared dealing with local order in glassy Pd-B alloy^,'^ amorphous-to-crystalline transformations in Ni-B alloy^,'^ and the effects of additives on the corrosion resistance of amorphous Fe-B allows.Is The first compound containing a B=C double bond (1) has been synthesized and spectroscopically characterized.l6 Its stability is rationalized by the presence of the four bulky substituents. The thermally stable three-membered BC2 ring borirene (2) and the four-membered B2C2 ring diboretene (3) have also been rep~rted.'~ Both are two-.rr-electron aromatics.On the basis of previous theoretical work it is suggested that (3) has a non-planar C,,geometry. Me I Me,Si \ C-C=B-CMe CMe '\/Me,Si B I Bu' ,Bu' 'c=c Me \/B I Bu' -ck B -.>C-But ~ -y B I Me (1) (2) (3) 2 Halides The laser-induced reaction between c6F6 and BC13 affords" mainly BC12F and C6F5Cl. Halide exchange has also been studied in the B2F4/B2C14 B2C14/B2Br4 and B2C14/B13 systems the last affording B~14.l~ BF3 reacts with the adducts Me,N.AlH or Me,N.GaH in the gas phase to yield BF2H by halide-hydride exchange.20 No evidence was found to support a previous claim that Lewis acid displacement affording Me3N-BF3 and GaH, occurs in the gallium system. Instead it is proposed that the reactions proceed according to equations (1) and (2) with subsequent decomposition of MH2F.lo T. Ohtani B. Chevalier P. Lejay J. Etourneau M. Vlasse and P. Hagenrnuller J. Appl. Fhys. 1983 54 5928. I' T. Ishii M. Shirnada and M. Koizumi J. Magn. Magn. Muter. 1983 31 151. l2 V. A. Shcherbakov and A. N. Pityulin Fiz. Goreniya VZ~~UQ 1983 19 108. I3 G. Cocco S. Enzo L. Schiffini L. Battezzati and A. Lucci GQZZ. Chim. Ira[. 1983 113 269. 14 C. Antonione L. Battezzati E. Lazoni and A. Lucci GQZZ. Chim. Ztal. 1983 113 293. l5 J.-P. Crousier J. Crousier Y. Massiani and C. Antonione GQZZ. Chim. ZtaL 1983 113 329. l6 H. Klusik and A. Berndt Angew. Chem. Znt. Ed. Engl. 1983 22 877. " S. M. van der Kerk P. H. M. Budzelaar A. van der Kerk-van Hoof G. J. M. van der Kerk and P. von R.Schleyer Angew. Chem. Znt. Ed. Engl. 1983 22 48. P. Engst M. Horak and J. Pola Collect. Czech. Chem. Commun. 1983 48 1314. I9 W. Haubold and P. Jacob Z. Anorg. Allg. Chem. 1983 507,231. 20 A. E. Shirk and J. S. Shirk Inorg. Chem. 1983 22 72. Boron 21 BF + Me3N.MH3 + Me3N.MH3BF3 (1) Me3N.MH,BF3 -BF,H + MHzF + NMe3 (2) M = Ga or A1 Recent developments in n.m.r. pulse sequencing have facilitated completion of the measurement of "N and "B spectra of the series of NMe adducts of the mixed boron trihalides BXiX' (X' X2 = F C1 Br or I in all permutations) and of Me,N.BC1BrI.21 A number of correlations are established most importantly that between J("B-"N) and the strength of the N-B bond. This is therefore a more useful (and is anyway more easily measured) parameter than S("N) which does not correlate well with the adduct bond strength.In the past S("B) has been employed to estimate the strength of the donor-acceptor bond in trihalogenoborane adducts and Martin et al. have used this parameter to confirm that the acceptor strength of BBr in a variety of pyridine adducts is greater than that of BF,. 'H N.m.r. data are also reported.22 Similarly spectroscopic studies of the complexes (4) derived from 1,2,3,4-tetrahydro- 1,lO-phenanthroline show a progressive N(pyridine)-B co-ordination in the series X = F C1 Br I., A crystallographic of (4; X = F) shows that the B-N co-ordinate bond 1.629(7) A is substan- tially longer than the other B-N bond 1.500(6) A. SiFMe,I N SiFMe,I Me2SiHN\SiMe2 I I N.HN .,N\s1 F /N\B Me2 .AH s1 BF,-etherate reacts with 2,2,4,4,6,6-hexamethylcyclotrisilazanesand their lithium salts to yield silaborazines or the BF-bridged species (5),as reported two years ago. Crystallographic of (5) has shown that the molecule has space-group required CZvsymmetry along the B-F bond 1.348(5) A and cyclotrisilazane rings of conformation intermediate between boat and twist. Adducts of halogenoboranes and SMe are known hydroboration reagents towards alkenes and it has now been shown26 that since addition of traces of free Lewis acid dramatically catalyses the hydroboration (by trapping free SMe,) the overall mechanism involves prior dissoci- ation according to equations (3)-(5). This mechanism explains the previously BHBr,-SMe BHBr + SMe (3) BHBr + alkene -RBBr (4) RBBr + SMe S RBBr,.SMe2 (5) R = alkyl 2' J.M. Miller Znorg. Chem. 1983 22 2384. 22 D. R. Martin J. U. Mondal R. D. Williams J. B. Iwamoto N. C. Massey D. M. Nuss and P. L. Scott Inorg. Chim. Acta 1983 70 47. 23 G. Klebe K. Hensen and J. von Jouanne J. Organometal. Chem. 1983 258 137. 24 G. Klebe K. Hensen and H. Fuess Chem. Ber. 1983 116 3125. 25 W. Clegg Acta Crystallogr. Sect. C 1983 39 387. 26 H. C. Brown and J. Chandrasekharan Organometallics 1983 2 1261. 22 A. J. Welch apparent anomaly that BHBr,-SMe is a faster hydroboration reagent than BHCl,*SMe, since dissociation of the weaker adduct RBC1,.SMe2 into RBCl and SMe2 has a larger rate-retarding effect. The continuing importance of BF3 as catalyst for a wide variety of chemical reactions is demonstrated by the following small selection addition of NF30 to alkenes to afford N,N-difluoro-0-perhalogenoalkylhydroxylamines;27 efficient and regiospecific coumarin photodimerization;28 low-temperature stereospecific car-bonylation of (7-C,H,)Fe(CO)(phosphine)( Me) complexes ;29 and the formation of 1,2-dioxolanes from the reaction between alkenes and o~onides.~' 19 F N.m.r.spectroscopy is used to distinguish between the co-ordinated and terminal tetrafluoroborate F atoms in (7-C,H,)M(CO),(L)(FBF,) [M = Mo or W; L = CO PPh, or P(OMe),] and to follow bridge-terminal exchange at elevated temperature.,' Crystallographic and i.r. spectroscopic study of the first example of a BF anion bridging two metal centres has been given,, for +Cu(bipy)FB( F),F-3 [BF,].The co-ordination geometry at the Cu" centre is elongated rhombic trans octahedral with asymmetric Cu- F distances of 2.560( 5) and 2.656(5) A complemented by B to p-F bond lengths of 1.372(5) and 1.395(6) A respectively. Consistent with this the i.r. spectrum of the complex shows at low temperature three peaks centred on 1100 cm-' due to local C,,symmetry. A useful compilation of crystallographic and i.r. spectra data for co-ordinated BF is given in this paper. 3 Boron-Oxygen Sulphur and -Selenium Compounds The reactions of B(OH) with the aliphatic amines diethylamine 2-aminoethanol ethylenediamine and hexamethylenetetramine in aqueous media have been investi- gated,, and a cyclic borate of stoicheiometry Et,NH.12B,O3.3H20 isolated from the boric acid-Et2NH system.34 B(OH) is produced by acid degradation of [B3H7( NCS)]- in the atmosphere and structural study of [( Ph,P),N]Cl.B(OH) shows that the association of B(OH)3 molecules into infinite sheets is prohibited by hydrogen-bonding with chloride ions.35 Enthalpies of formation of 1 :1 and 1 :2 complexes of B(OBu) with SbC1 and TiC14 have been measured and not unreasonably are ca. twice for the Sb species what they are for the Ti complex.36 Raman spectra of alkaline solutions of lithium metaborate containing peroxide are consistent with an equilibrium between [B(OH)J and [B(OH),OOH]- anions,37 according to equation (6). B(OH) + H202 B(OH),(OOH)-+ H,O (6) 27 R.D.Wilson W. Maya D. Pilipovich and K. 0. Christe Inorg. Chem. 1983 22 1355. 28 F. D. Lewis D. K. Howard and J. D. Oxman J. Am. Chem. SOC. 1983 105 3344. 29 H. Brunner B. Hammer I. Bernal and M. Draux Organornetallics 1983 2 1595. 30 M. Yoshida M. Miura M. Nojima and S. Kusabayashi J. Am. Chem. SOC. 1983 105 6279. 31 K. Sunkel G. Urban and W. Beck J. Organometnl. Chem. 1983 252 187. 32 J. Foley D. Kennefick D. Phelan S. Tyagi and B. Hathaway 1. Chem. Soc. Dalton Trans. 1983,2333. 33 R. S. Tsekhanskii V. G. Skvortsov and A. K. Molodkin Zh. Neorg. Khim. 1983 28 859. 34 V. G. Skvortsov R.S.Tsekhanskii A. K. Molodkin V. M. Akimov 0.V.Petrova and V. P. Dolganev Zh. Neorg. Khim. 1983 28 1313. 35 S. J. Andrews D. A. Robb and A. J. Welch Acta Crystallogr.Sect. C 1983 39 880. 36 V. G. Tsvetkov V. P.Maslennikov N. G. Chernaya E. E. Grinberg and Yu. A. Aleksandrov Zh. Prikl. Khim. 1983 56 1922. 37 C. J. Adams and I. E. Clark Polyhedron 1983 2 673. Boron 23 The accurate electron density distribution in LiBO, which contains infinite chains of B03 triangles between which lie the lithium atoms has been determined. Interpre- tation of the deformation-density leads to a simplified bonding model of the LiB0 sub-unit which polymerizes into the observed structure.38 Isolated rather asym- metric B03 units are found in Pb40[Pb2(B03)3C1] for which a crystal structure and i.r. spectrum are reported.39 Bz03 reacts4’ with excess SO3 in sealed tubes to yield ‘B2O3.SO3’ at 90-95 “C and ‘B2O3.2SO3’ at 200 “C; i.r.and “B n.m.r. spectroscopic study4’ of these products does not yield unambiguous structures but does indicate that both species contain B03 and B04 units. H2L[B405(OH),] (L = ethylenediamine) results from reaction between aqueous B203 and excess ligand or by thermolysis of B(OH)3 with L.42 The hydrated magnesium borate ‘Mg0.3B2O3-7.5H,O’ has been isolated43 from borate-containing magnesium chloride brine and the B205 unit in both crystal modifications of anhydrous magnesium pyroborate ‘2Mg0-B2O3’ has been the subject of a thorough vibrational analysisa which has identified a marked difference in force constants between terminal and bridging B-0 bonds. In Tl[B304(OH)2].0.5H20 there are [B3O4(OH),]- units linked into an infinite chain [B30,(OH),]~m.Dehydration occurs in two steps affording first (453 K) Tl[B304(OH),] and then (493 K) TlB305?5 The thermolysis of borax Na,[B405(OH),].8H20 continues to be a subject of research interest. The product after complete dehydration Na20-2B203 is reported46 to decompose at 700 “C to yield NaBO vapour and B203. The system KF-B(OH)3-H20 has previously been shown to produce ‘KFsB(OH)~’ alternatively described as a salt K[BF(OH),] or as a triple F.-H bonded array. It has been demonstrated that an excess of B(OH) in the system affords the previously known borate K[B506(OH)4].2H20 and the possible role of F-as catalyst (rendering by OH- -.F bond formation the oxygen more nucleophilic and therefore more likely to attack a second boron centre) in its formation is discussed.High-field (127 and 160 MHz) I’B n.m.r. of aqueous polyborate equilibria have allowed calculation of formation constants for [B(OH),]- [B303(OH),]- and [B506(OH),]- [see equations (7)-( 1O)] ;in parallel temperature- and concentration- dependent dissociation of the polyborate species has been studied. Limitations of 38 A. Kirfel G. Will and R. F. Stewart Acta Crystallogr. Sect. B 1983 39 175. 39 H. Behm Acta Crystallogr. Sect. C,1983 39 1317. 40 S. N. Kondrat’ev S. I. Mel’nikova and A. M. Bondar Zh. Neorg. Khim. 1983 28 851. 41 A. M. Bondar S. N. Kondrat’ev and S. I. Mel’nikova Zh. Neorg. Khim. 1983 28 855. 42 G. Ozolins R. V.Zinchenko and E. Silina Latv. PSR Zinat. Akad. Vestis. Kim. Ser. 1983 294. 43 S. Gao J.Zhao F. Xue and T. Hu Huaxue Xuebao 1983,41 217. 44 Yu. N. Win V. V. Kravchenko and K. I. Petrov Zh. Neorg. Khim. 1983 28 1609. 45 M. Touboul C. Bois D. Mangin and D. Amoussou Acta Crystallogr. Sect. C 1983 39 685. 46 E. Hartung K. Heide R. Naumann K. H. Jost and W. Hilmer J. Ilherm. Anal. 1983 26 277. 47 J. Emsley and J. S. Lucas J. Chem. Soc. Dalton Trans. 1983 181 1. 48 C. G. Salentine Inorg. Chem. 1983 22 3920. A. J. Welch the method however are that no signals were detected for the [B4O5(0H)J2- ion which must be present equation (9) and that only one boron environment is suggested for [B506(OH)4]-. In Na6CO3[B,07(0H),],.26H,O there are two different types Of [B&(OH)6] co-ordination to the transition Co( 1) is centrosymmetrically bonded to two water molecules and uia two Co-O(H) bonds to two polyborates whereas Co(2) (which occurs twice as frequently in the crystal lattice) is sandwiched between two polyborates each involved in three Co-O(H) bonds.Both modes of [B607(OH)6] co-ordination have been observed previously but their coexistence in one species serves to highlight the stereochemical diversity available in this area of boron chemistry. Two completely novel relatively large polyborate anions have been reported. In the first [B8OI2( OH),],- structurally studied as Tl,[borate].H,O there are four B04 tetrahedra and four B03 triangle^,^' and the structural formula is best represented as [B7010(OH)3.0BO(OH)]4- these units being linked together into an infinite chain.In contrast discrete anions exist of {CU~[B~~~~~(OH) (6) structurally studied5' as N~,(CU~[B~,~~,(OH)~~]}. 12H20. In (6) there are eight Bo3 triangles and eight B04 tetrahedra surrounding two planar Cu centres to afford the largest discrete polyborate anion yet reported. (6) (Reproduced by permission from Acfa Crystallogr. Sect. C,1983 39 20) Potassium bis-(4-methylcatecholato)borate surprisingly precipitates from a slightly basic very dilute aqueous solution of B(OH)3 and ligand and this result has prompted a general discussion of equilibria in the boric acid-catechol system.52 Alkylboronic esters R' B( OR2)2 transfer the alkyl group R' from boron to carbon by reaction53 with methoxy(pheny1thio)methyl-lithium subsequent oxidation of the product R1CH(OMe)B(OR2)2 affording the aldehyde R'CHO.This homologation of boronic esters as a synthetic method in chiral organic syntheses is an important area and one of much current activity due largely to the efforts of Matteson and 49 H. Behm Actu Crystullogr. Sect. C,1983 39 1156. M. Touboul C. Bois and D. Amoussou J. Solid Sfate Chem. 1983 48,412. 51 H. Behrn Acta Crystallogr. Sect. C 1983 39 20. 52 L. Babcock and R. Pizer Inorg. Chem. 1983 22 174. 53 H. C. Brown and T. Imai J. Am. Chem. Soc. 1983 105 6285. Boron 25 co-workers. It is however outwith the intended scope of the present Report and we therefore refer interested readers to references 54-60. The stable bridged borate ester B(OCH2C3H4CH20)B (7) has been synthesized and structurally characterized.6' The molecule has overall C3 symmetry and the cyclopropane bridges give the molecule helicity thus affording a conformationally stable symmetric species which has accordingly been studied by FT i.r.Raman and vibrational circular dichroism spectroscopy. (7) (Reproduced by permission from Inorg. Chem. 1983 22 23 19) Important recent developments in boron sulphide boron selenide and thioborate chemistry have been lucidly reviewed by Krebs.62 One of the compounds featured in this review is the macrocycle B8S16 first synthesized in 1980. Its electronic structure was analysed at the Huckel level in 1982 and now the same workers have re-evaluated the molecule with particular reference to possible complex formation by extended Huckel (EH) MO calculation^.^^ If the basis set includes sulphur 3d AOs with a coulomb integral value of -8 eV a Cu2+ centre is bound by the macrocycle about as strongly as it is by porphine but if the integral is set at only -4 eV the calculated Cu-S bond strength drops by about two-thirds.The synthesis and 13C n.m.r. spectra of five dialkylamino(ethy1thio)phenylboranes have been reported.64 Rotation about the B-N bond is considered more restricted 54 D. S. Matteson and K. M. Sadhu J. Am. Chem. SOC. 1983 105 2077. 55 D. S. Matteson and D. Majumdar Organornetallics 1983 2 230. 56 D. J. S. Tsai and D. S. Matteson Organometallics 1983 2 236. 57 D. S. Matteson and D. Majumdar Organometallics 1983 2 1529. 58 D. S. Matteson and E. Erdik Organometallics 1983 2 1083.59 D. S. Matteson R. Ray R. D. Rocks,and D. J. Tsai Organometallics 1983 2 1536. 60 D. J. S. Tsai P. K. Jesthi and D. S. Matteson Organometallics 1983 2 1543. 61 V. J. Heintz W. A. Freeman and T. A. Keiderling Inorg. Chem. 1983 22 2319. 62 B. Krebs Angew. Chem. Znt. Ed. Engl. 1983 22 113. 63 B. M. Gimarc and J.-K. Zhu Znorg. Chem. 1983 22 479. 64 R. H. Cragg and T. J. Miller J. Organometal. Chem. 1983 243 387. A. J. Welch in these species than in analogous alkoxy-compounds since the B-S .n-bond is less strong than that between B and 0. Two routes to arylboronic acids have been described. One-pot synthesis is afforded by the reaction between arylmagnesium halides and borane compounds followed by hydr~lysis,~~ and ortho-lithiation of substituted benzylamines and reaction with trimethylborate allows synthesis of arylboronic acids with intramolecular N -B bonding.66 Such bonding occurs in (8) (R = H or Me) but not when R = Ph as evidenced by ‘H and IlB n.m.r.data.67 A temperature-dependent fluctionality in the adduct bonding between a variety of amines and either triethyl- or triphenyl-boroxine is shown by n.m.r. studies and this has been interpreted in terms of the low- temperature limiting spectrum being that in which only one boron is bound to nitrogen (9). This supposition is entirely consistent with the results of a crystallo- graphic determination68 of 2(PhBO),-3(p-H,NC6H,NH2) which has a B :N ratio of I 1 but is such that one phenylenediamine molecule bridges two boroxines leaving two free amines of solvation (10).(8) (9) R = Et or Ph CY (10) (Reproduced permission form Gem.Ber. 1983 116 3347) 65 G. W. Kabalka U. Sastry K. A. R. Sastry F. F. Knapp jun. and P. C. Srivastava J. Organometal. Chem. 1983 259 269. 66 M. Lauer and G. Wulfe J. Organometal. Chem. 1983 256 I. 67 R. Contreras C. Garcia T. Mancilla and B. Wrackmeyer J. Organometal. Chem. 1983 246 213. 68 M. Yalpani and R. Boese Chem. Ber. 1983. 116 3347. Boron 27 4 Boron-Nitrogen -Phosphorus and -Arsenic Compounds An improved synthesis of a crystalline poly( aminoborane) ( H,NBH2) has been described and on the basis of its X-ray powder pattern and very low solubility it is supposed that the species is either a cyclic or linear polymer of relatively high molecular Two forms of methyleniminoborane H2C=N-BH2 have been investigated by geometry-optimized ab initio MO cal~ulations.~~ The linear orthogonal form (1 1) is more stable than the planar bent form (12) by 46.9 kJ mol-' which contrasts with (1 1) (12) results of the (previously studied) isoelectronic H2B-0-BH2.In (1 1) bond lengths and electron population analyses support strong N-B .rr-bonding. In B( N=CBU~~)~ (13) the stereochemistry is such that the NCBut units are all perpendicular to the central plane thereby allowing for overall maximal N -D B v-b~nding.~' Thus the orthogonality of B and C co-ordination planes in (13) parallels that in (1 1). The N-B distance in (13) is 1.39(2) A and C-N is 1.23 A.An alternative bonding mode for imines is that of a bridging 3-e ligand as found in the centrosymmetric dimer (14) reported in the same communication. Me Me Me Me (14) R = Me or Ph Molecular Orbital Bond Index '(MOBI) calculations have been used72 to probe preferred geometries of N( BH2)3 and B,( NH,),. Unfortunately there are serious typesetting errors and/or inconsistencies in the paper that result in this reviewer being unable fully to correlate figures tables and text. What is clear (I think) is that N( BH2)3 is most stable with one BH2 unit coplanar with the central NB3 moiety and the other two perpendicular to it and that B6( NH2) is most stable with a planar B6 ring which contrasts with the established chair conformation in the crystal structure of B6( NMe2),.Charge distribution in BH2R H3N*BH2R RH2N and RH,N-BH has been calculated73 by four methods (CNDO MNDO Jolly and 69 R. Komm R. A. Geanangel and R. Liepins Inorg. Chem. 1983 22 1684 2222. 70 G. Gundersen and S. Saebo Acta Chem. Scand. Sect. A 1983,37 277. 7' J. R. Jennings R. Snaith M. M. Mahmoud S. C. Wallwork S. J. Bryan J. Halfpenny E. A. Petch and K.Wade J. Organometal. Chem. 1983 249 CI. 72 A. Neckel H. Polesak and P. G. Perkins Inorg. Chim. Acta 1983 70 255. 73 W. Linert V. Gutmann and P. G. Perkins Inorg. Chim. Acta 1983 69 61. A. J. Welch Perry and modified Sanderson) and for the adducts only the last is found to be reasonably concordant with experience. In the adduct of BBr3 with pyridine the N-B co-ordinate bond is 1.59(2) A.74 Polarographic reduction of substituted trimethylamine- N-pyridylboronium cations has been f~llowed,~' and N-co-ordination of inter ah the BEt function to 4,4'-bipyridyl affording the radical cation (19 has been studied with a view to possible control of the redox properties of the liga~~d.~~ Full details have now been reported7' of variable-temperature I3C n.m.r.spectro- scopic studies of the series of aminoboranes PhB(X)-NR2 (X = F C1 Br OMe or SEt; R = Me or Pri) used to delineate steric and electronic effects upon the barrier to rotation about the B-N bond. The series chosen for study is particularly interesting in that conflicting sequences exist within with regard to the ease of rotation.A further paper from the same group7* reports aminoboration of phenyl isocyanate by 27 aminoboranes where X is additionally extended to NH2 and NHR. Clearly there are two potential products PhB(X)N(Ph)C(0)NR2 or PhB( NR,)N(Ph)C(O)X depending upon the relative migratory aptitude (RMA) of NR2versus X. It is found that RMAs decrease in the series BuNH > N(CH2)3CH2> N(CH2)4CH2> Me2N > Et,N > Bu'NH > N(CH,),CHMe > Pri2N and RS > RNH > R2N > OR halide or Ph. Thermolysis of diarylaziodoboranes Ar,BN3 affords either diazadiboretidines (16; R' = R2 = Ar) or borazines (ArBNAr)3 via boryltetra-azaborolines (17) and with BEt isomeric diboronylamines (IS) and (19) are produced. The possible inter- mediacy of boron imides ArB=NAr in these reactions has been discussed.79 The imide Bu"B=NBu' (20) dimerizes to (16; R' = But R2 = Bun) in the presence of a catalytic amount of t-butyl isocyanide and the product may be stabilized by q4-co-ordination to either a Cr(CO) or W(CO)4 unit.80 A crystal structure determi- nation of the Cr complex reveals that the N atoms are trans to CO with the boron atoms bent away from the metal [Cr-B 2.354(4) 2.361(4)A Cr-N 2.205(2) 74 K.Iijima I. Oonishi and S. Shibata Chem. Leff. 1983 251. 75 K. Zutshi G. E. Ryschkewitsch and P. Zuman Inorg. Chem. 1983 22 564. 76 W. Kaim J. Organometal Chem. 1983 241 157. 77 C. Brown R. H. Cragg T. J. Miller and D. O'N. Smith J. Organometal. Chern. 1983 244 209. 78 R. H. Cragg and T. J. Miller J. Organomefal.Chem. 1983 255 143. 79 P. Paetzold and R. Truppat Chem. Ber. 1983 116 1531. 80 K. Delpy D. Schmitz and P. Paetzold Chem. Ber. 1983 116 2994. Boron 29 Ar\ Et ,B-N\ BEt2 /Ar Ar Et \/B-N/\Ar BEt2 Bu'Bun\ /B-N I 1 N-P \ (18) (19) R2/ NR (21) a; R' = R2 = SiMe b; R' = Pri R2 = But 2.210(2) A] leading to a BNBN ring which is folded by 21.9" about N...N . With iminophosphanes (20) affords (21) by cycloaddition.81 Electrophilically induced substitution reactions at boron of pyrazaboles (22) have been studied and an extensive range of derivatives has been synthesized. Molecular structures determined for (22) with R' = R2 = R3= R4 = Cl Y = H; R' = R2 = R3 = R4 = SMe Y = H; R'R2 = R3R4 = SCH2CH2S Y = H; R' = R3 = Ph R2 = R4 = N2(CH),CH,Y = H;andR' = R4 = Br,R2 = R3 = H,Y = Clsuggest that the potential for deformation of the central B2N4 ring is rather soft since a number of different conformations are observed.82 The synthesis and reactions of I ,3-dimethyl-2-(pyrazol-1'-y1)-1,3-diazaboracyclopentanes have been studied in recent years.In 1983 the equivalent cyclohexane derivatives (23) have been prepared and it is found that the Lewis acidity of the boron atom of (23) is considerably less than that of the former species presumably as a consequence of the wider annular NBN angle.83 Complete assignment of the 13C n.m.r. spectra of the substituted borazine [MeBN( o-tolyl)] and the related heterocycle (24) have been reported and the chemical shifts of the latter correlated with charge densities from HMO calcula-tion~.~~ The molecular structures of the 19e complexes (25)8s and (26)86 have been determined.In (25) there are two crystallographically independent molecules each with Cisymmetry whereas (26) exists in two conformations corresponding to clockwise and anticlockwise arrangements of the azaborolinyl rings. In all four species the formal electronic excess at Co is somewhat relieved by slipping of the " P. Paetzold C. von Plotho E. Niecke and R. Ruger Chem. Ber. 1983 116 1678. a2 K. Niedenzu and H. Noth Chem. Ber. 1983 116 1132. F. Alam and K. Niedenzu J. Organometal. Chem. 1983 243 19. 84 S. Allaoud H. Bitar M. El Mouhtadi and B. Frange J. Organometal. Chem. 1983 248 123. 85 G. Schmid U. Hohner D. Kampmann D. Zaika and R.Boese J. Organometal. Chem. 1983,256,225. 86 G. Schmid and R. Boese Z. Naturforsch. B Anorg. Chem. Org. Chem. 1983 38 485. A. J. Welch I -Me ligands such that B and N atoms are further from the metal than are C atoms. (25) and (26) are readily oxidized to 18e monocations by either I or [(q-C,H,),Fe]+. Paramagnetic Mn" and Co" bis-ligand complexes of the (dimethylmethyl-enephosphorany1)dihydroborate anion (27) have been synthesized. The ligand is an excellent a-donor and minimal wacceptor. Magnetic data are reported in solution for both and in the solid for the cobalt complex and a single -crystal X-ray diffraction study of the manganese species (the Co analogue is isomorphous) confirms tetrahe- dral geometry and shows that both six-membered rings have chair conformation^.'^ (27) (28) Cyclenphosphorane reacts" with B,H to yield the bis-adduct (28) a surprisingly stable species and the first established example of a molecule with the sequence H,B-N-P-N-BH,.BH adducts of transition-metal substituted arsanes (q-C5H5)M(L)(C02)As(Me),BH,(29) (M = W or Mo L = CO or PMe,) have been prepared by reaction between the metal complex and H,B.THF. Treatment of (T-C~H,)MO(CO),AS(M~),BH, with PMe affords both (29; M = Mo L = PMe,) by CO substitution and (T-C~H,)MO(CO)~ASM~~Me,P.BH3 by BH, plus ab~traction.'~ 5 Heterocyclic Derivatives The ability of BX (X = typically halide alkyl or aryl) groups to bridge the oxygen atoms of transition-metal bis-( a-dioFimato) c?mplexes and form stable macrocyclic species with heterocyclic functions MNOBON is well established and continues to be of irnportan~e.~~ It has recently been shown that additionally such groups can act as linking functions between two such metal comple~es.~' Chelation of the BX2 group by N-alkyl- or N-aryl-hydroxamic acids affords the heterocyclic compounds (30) synthesized9 for various X R' and R2,and discussed in terms of the resonance structures shown.An analysis of bond lengths in two crystallographically studied9 examples (31 ; R3= R" = H) and (31 ; R3= Me 87 G. Muller D. Neugebauer W. Geike F. H. Kohler J. Pebler and H. Schmidbaur. Organometallics 1983 2 257. 88 J.-M. Dupart S. Pace and J. G. Riess J. Am. Chem. Soc. 1983 105 1051. 89 R. Janta R. Maisch W.Malisch and E. Schmid Chem. Ber. 1983 116 3951. 90 F. S. Stephens and R. S. Vagg Inorg. Chem. Acra 1983 69 103. 9' M. L. Bowers and C. L.Hill Inorg. Chim. Acta 1983 72 149. 92 W. Kliegel and D. Nanninga Chem Ber. 1983 116 2616. 93 W. Kliegel D. Nanninga S. J. Rettig and J. Trotter Can. J. Chem. 1983 61 2493. Boron 31 /\ /\ Ph Ph Ph Ph a b (31) R4 =C6Hll),suggests that although both forms are important the B,N-betaine structure (b) is dominant. A following paper94 by the same group describes the synthesis and structure of bis[salicyladoximato(2-)phenylboron] shown to contain the first crystallographically studied B2N202ring (as one of five fused six-membered rings). Molecular parameters are discussed in terms of contributions from four resonance structures (32a-d).Ph Ph Ph Ph a b In attempting to synthesize the B2N202ring-containing dimer of (isopropy- 1ideniminoxy)diphenylborane from acetone oxime and oxybis(dipheny1borane) many years ago it was found that an adduct was produced containing phenylboronic acid and diphenylboronic acid moieties. However extensive chemical and spectro- scopic study could not distinguish between structures (33a) and (33b) for this adduct. Now crystallographic analysis has unambiguously established (33a) as correct.95 Me Me Ph \ +AB/Ph \ +,o,-/ C=N B-Ph /“=Y 1 \I Me ,B-0 Me / Ph I /B-o Ph Ph a b (33) 94 S. J. Rettig and J. Trotter Can. J. Chem. 1983 61 206. 95 W. Kliegel D. Nanninga S. J. Rettig and J. Trotter Can.J. Chem. 1983 61 2329. A. J. Welch Molecular structures have also been determined96 of the five- and six-membered heterocycles (34) (34)-B(Ph),PH solvate and (35) and a correlation is established between the lengths and the rates of hydrolytic cleavage of the N-B bonds in (34) (35) and (36). (36) R = H F or Me Seven-membered BOCCCNO heterocycles with the B,N-betaine structure (37) have been ~ynthesized~~ from nitrones of salicylaldehyde by entirely analogous routes to those leading to (30) and six-membered analogues (38) are affordedg8 by reaction of 2-formylphenylboronic acid with N-substituted hydroxylamines followed by esterification. With phenylboronic acid and formaldehyde RN( H)OH yields the bicyclic species (39) characterized spectroscopically99 for R = Me Et Pr" Pr' C6H11 and CH2Ph.H \ -/ f-J.+R\ B'Od=;\fO'B XIX 0 (37) (38) R PhB 1 P-NqNRI 04:-0' Ph (39) Octahydroxycyclobutane reacts with trialkylboranes dichloro-organoboranes and trialkylboroxines to yield'" the pentaheterocyclic product (40). In the presence of Et2BC(0)OBu' the thermochromic species (41 ;R = Et) is also formed by cleavage of the cyclobutane ring and following up this observation Yalpani and Koster have additionally synthesized a range of products (41) from dihydroxybutenedioic acid and boron substrates."' When R is an n-alkyl or iso-alkyl group (41) is thermochromic being colourless when 'hot' and yellow when 'cold'. For R = t-alkyl or aryl however (41) is colourless even to 4 K. Crystal structureslo2 of (41;R = Et) at 40 "C and -30 "C and for comparision of (41; R = Ph) at room temperature RR (40) (41) 96 S.J. Rettig and J. Trotter Can. J. Chem. 1983 61 2334. 97 W. Kliegel and D. Nanninga J. Organometal. Chem 1983 243 373. 98 W. Kliegel and D. Nanninga J. Organometal. Chem. 1983 247 247. 99 W. Kliegel J. Organometal. Chem. 1983 253 9. 100 M. Yalpnai R. Koster and G. Wilke Chem. Ber. 1983 116 1336. 101 M. Yalpani and R. Koster Chem Ber. 1983 116 3332. I02 M. Yalpani R. Boese and D. Blaser Chem. Ber. 1983 116 3338. Boron 33 have shown that the yellow colour of the 'cold' form results from intermolecular bonding between the boron atoms of one molecule with carbonyl oxygens of adjacent ones in concert with a bend-back of pendant ethyl groups.1,2-Dihydro- N-substituted- 1 -aza-2-borabenzenes are compounds of pharmaco-logical interest and the synthesis of N-phenyl analogues from PhBC1 and the corresponding a,P-unsaturated o-aryl azide has recently been reported. lo3 The adduct Me3N-BH,CH2SMe decomposes upon heating to yieldlo4 the dithiodiboracyclohexane derivative (42) whose n.m.r. spectra show the presence of two isomers corresponding to both methyl groups axial or equatorial; in the solid state the latter is found. H7 x-Ph The reactions of 1-X-4-boracyclohexa-2,5-dienes (43) obtained from the radical- initiated reaction between Et,NB(C_CR) and H,XPh have been ~tudied.'~' Partial hydrogenation of the arsenic compound is possible with additional H2AsPh.The B-bonded exocyclic function may be substituted stepwise by OMe and But and X may be alkylated after cleavage of the X -Ph bond by alkali metals. Phosphorus(v) derivatives with additional P=E (E = 0 S or Se) bonds may also be obtained. In the final part of this section we concentrate on a number of transition-metal complexes with m-bonded B,C heterocyclic ligands. Occasionally their strict classification as heterocyclic derivatives is tenuous since especially when the B :C ratio is relatively high a case could be argued for regarding them as polyhedral carba(metal1a)boranes. This is of course perfectly reasonable and it is right that there should be no rigid boundaries between areas. Palladino and Fehlner have synthesized'06 (7-CsHs)Co( q-C4Ph4BH) in,ca.20% yield by reaction of the metallacyclobutadiene (r]-CSH5)(PPh3)Co(CPh),CPh with BH,.THF and suggest that this synthetic approach to carbon-rich carbametal- laboranes has potential. An interesting complement to this work is f~rnished"~ by the generation of nido-[l-I-2 3 4 5 &Me5-& 3 4 5 6,-CsB]+ (writing it as a cluster) from [(r]-CSMe5)Sn]+ (writing it as a metal-ligand complex) by reaction with B13. Ethene displacement from (T-C,H~)CO(C~H~)~ by 1,3-diborolenes affordslog com- plexes (44). In (44) the axial H atom of the endocyclic methjrlene carbon C-2 is acidic and facile deprotonation affords monoanions which are readily alkylated. A molecular structure of (44a) shows that C-2 is formally five-co-ordinate and semi- empirical MO calculations reveal a frontier orbital which is three-centre C0-C 2-H from whose form it is clear that strong Co-C-2 bonding is directly responsible for weak C-2-H bonding (and thus acidic H).Therefore the formal diborolene 103 R. Leardini and P. Zanirato J. Chem. SOC. Chem. Commun. 1983 396. 104 H. Noth and D. Sedlak Chem. Ber. 1983 116 1479. 105 H.-0. Berger and H. Noth J. Organometal. Chem. 1983 250 33. I06 D. P. Palladino and T. P. Fehlner Organometullics 1983 2 1692. 107 F. Kohl and P. Jutzi Angew. Chem. Int. Ed Engl. 1983 22 56. log J. Edwin M. C. Bohm N. Chester D. M. Hoffman R. Hoffmann H. Pritzkow W. Siebert K. Stumpf and H. Wadepohl Organometullics 1983 2 1666. A. J. Welch ligand of (44) is appreciably perturbed towards the more common diborolenyl form of which many examples are known.The anionic (44b)- with SnC12 afford^'^' the bent quadruple-decker complex [( q-C5H5)Co( q-C2Et2B2Me2CH)],Sn in which the Co-Sn vectors interesect at 130"; the bent geometry of this complex is broadly similar to that of (q-C,H,),Sn. Et (44) a; R' = Et R2= Me b; R' = Me R2 = H Syntheses reactivities electrochemistries and solid-state structures of and bond- ing within triple-decker 1,3-diborolenyl complexes with 29-34 valence electrons have been the subject of a very extensive study by Siebert Geiger Kruger Bohm and co-workers.'" The complexes studied are (q-C,H,)M'[p-( q-C,B2H,)]M2( q-C5H5) with M'M2 = FeCo+ (29 valence electrons) FeCo (30) CoCo (31) CoNi (32) NiNi (33) and NiNi- (34).Triple-decker complexes (OC)3Mn(p-L)Mn(C0)3 and (7-C,H,)Fe(p-L)Fe( q-C5H5) (L = 2-ethyl-l-phenylborole), each of which has 30 valence electrons have been prepared and structurally and spectroscopically characterized.' '' Formed with the latter is the borabenzene derivative (q-C5H,)Fe(2-MeC,H,BPh) ;the synthesis and substitution reactions of the interesting boraben- zene/butadiene cobalt complexes (45) form the basis of a separate Finally the preparation and spectroscopic characterization of the metal complexes M(CO) (M = Cr Mo or W x = 4; M = Fe Ru Os x = 3) of the q6-1,4-diferrocenyl-l,4-diboracyclohexa-2,5-dieneligand have been described.'I3 R' >-( R' co R' (45) R' R2 = Me or Ph 6 Boranes and Derivatives The mechanism of the reaction of ethene with the adduct H3B.0H2 has been studied by ab initio MO calculations as a model for hydroboration in ether solvents."4 As I09 H.Wadepohl H. Pritzkow and W. Siebert Organometallics 1983 2 1899. 'Io J. Edwin M. Bochmann M. C. Bohm D. C. Brennan W. E. Geiger C. Kruger J. Pebler H. Pritzkow W. Siebert W. Swiridoff H. Wadepohl J. Weiss and U. Zenneck J. Am. Chem. SOC.,1983 105 2582. Ill G. E. Herberich J. Hengesbach G. Huttner A. Frank and U. Schubert J. Organometal. Chem. 1983 246 141. 1 I2 G. E. Herberich and A. K. Naithani J. Organometal. Chem. 1983 241 1. I13 G. E. Herberich and M. M. Kucharska-Jansen J. Organometal. Chem. 1983 243 45. I14 T. Clark D. Wilhelm and P. von R. Schleyer J. Chem. SOC.,Chem.Commun. 1983 606. Boron 35 shown in Scheme 1 the transition state involves an SN2-like displacement of the solvent by the alkene so that all four valence orbitals of the boron atom are always utilized. 9 "H 9 .Ji H \ ,--\ ,B,H H--C(1)-C(2>-H H/ \ t H H-. .-H )C( 1)=c(2); H H Scheme 1 Radiolysis of NaBH at 77 K affords the -BH4 radical e.s.r. parameters for which are reported and interpreted in terms of a C,,distorted geometry (in agreement with the conclusions of a parallel MNDO ~tudy)."~ The .BH4 radical is proposed to be an intermediate in the U.V. photolysis of the hydroborate anions BH4- [BH3(CN)]- and [BH(OBu'),]- in liquid ammonia rapid proton loss then affording the appropriate radical anion.'I6 Borane radical anions have previously been gener- ated from hydroborates by H atom abstraction+using alkoxy-radicals,' I7 and the same technique affords amine-boryl radicals J3N- BH from amine-borane com-plexes."' Analysis of the e.s.r.spectra of Et3N-f3H2 and Et,P-bH suggests that the geometry at B is pyramidal in the former and planar in the latter. Both the borane radical anion and its amine and phosphine complexes react with alkyl halides to give alkyl radicals."77118 Diffusion coefficients of BH4- at temperatures from 286 K to 313 K in aqueous solution at pH 12 have been reported and the diffusion control of the limiting current (dropping mercury electrode) has been established.' l9 Gyori and Emri have reported the synthesis of novel cyano- and isocyano-derivatives of BH3 and of BH4- generally in good yields.'20,'21 Specifically the dicyano anion [BH2(CN),]- is described for the first time. Super-tritide the tritiated analogue of the well known super-hydride LiEt,BH has been prepared and shown to have much the same powerful and stereospecific reducing properties as its hydride parent;'22 it thus appears to be a superior tritium labelling reagent to either NaBT or LiAlT,. Coulometric titration of adducts of diborane with oxidants such as bromine iodine or hypoiodite has been suggested as a suitable method for the determination of dib~rane.',~ 'Is M. C. R. Symons T. Chen and C. Glidewell J. Chem. Sac. Chem. Commun. 1983 326. 'I6 J. A. Baban J. C. Brand and B. P. Roberts 1. Chem. SOC.,Chem.Commun. 1983 315. I17 J. R. M. Giles and B. P. Roberts J. Chem. SOC.,Perkin Trans. 2 1983 743. I I8 J. A. Baban and B. P. Roberts J. Chem. Sac. Chem. Commun. 1983 1224. I I9 C. Biondi and L. Bellugi Gazz. Chim. Ital. 1983 113 525. I20 B. Gyori J. Emri and 1. Feher J. Organomeral. Chem. 1983 225 17. 121 J. Emri and B. Gyori J. Chern. SOC.,Chem. Commun. 1983 1303. I22 S. Hegde R. M. Coates and C. J. Pearce J. Chem. Soc. Chem. Commun. 1983 1484. I23 0. D. Kuleshova and A. I. Gorbunov Zh. Neorg. Khim.. 1983 28 83. A. J. Welch In 1982 an X-ray diffraction study showed that the [B2H7]- ion [as its (Ph3P)2N+ salt dichloromethane solvate] had a bent B -H -B bridge and overall C symmetry (46). Recent MO calculations to a very high level of sophistication (complete geometry optimization with a 6-3 1G**basis set and corrections for electron correla- tion using fourth-order perturbation theory) have confirmed the preference for a bent bridge system (although the potential surface to bending is rather flat) and shown that a bent ion with overall C2 symmetry (47) is equally ~tab1e.I~~ The triangular radical anion [B3H7]-' has been generated from [B,H,]- (H atom abstrac- tions using ButO*; see above) and e.s.r.data have been re~0rted.l~~ Tandem semi-empirical MO calculations suggest a structure of CZvsymmetry with a single B-H-B bridge (48). HH fR*,' The variety and complexity of the shapes of and possible substitution patterns in three-dimensional (polyhedral) boranes have led Casey Evans and Powell to seek a method of unambiguously describing and naming such species their analogues and their derivatives.Following earlier papers (1981) in which a descrip- tor system for closed polyhedra was established these authors have now expanded that system to encompass capped polyhedral 26 and have suggested nomenclature rules for closed'26 and non-~losed'~~ clusters. The rules outlined do not necessariy afford unique names but once derived they are unambiguous and structurally informative. As an example two descriptions of BgHl2 (49a) follow (i) (2,3-pH),(2,6-pH),(3,7-pH),(4,5,-pH)-1 v64v422) 1-deb~r[C~~-( -A'4-closo]nonaborane (ii) 1-debor[C2"-(1v64v222)-A14-~l~~~]nonaborane( 12)-2,3:2,6:3,7:4,5-pH4 An interesting alternative method of notation in clusters has been outlined by Hendon and Leonard in which a totally numerical description ('linear notation') of the polyhedral structure is achieved.'28 Unfortunately the linear notation and its shorthand version (which could serve as a unique registry number for use in data base searches etc.) are derived from a canonical numbering scheme that differs from that of Powell et al.Thus for numbered as in (49b) the linear notation is (0501)0203050604(0501)04070803(0501)08095 (0501)06 1007( 0501 )091 106( 0501) 1 110( 0501 )1208(0501) 12 (01)(01)(01)(O 1) I24 K. Raghavachari P. von R. Schleyer and G. W. Spitznagel J. Am. Chem. SOC.,1983 105 5917 12' J. M. R. Giles V. P. J. Marti and B. P. Roberts J. Chem. SOC.,Chem.Commun. 1983 696. 126 J. B. Casey W. J. Evans and W. H. Powell Inorg. Chem. 1983 22 2228. 127 J. B. Casey W. J. Evans and W. H. Powell Inorg. Chem. 1983 22 2236. I28 W. C. Herndon and J. E. Leonard Inorg. Chem. 1983 22 554. Boron 37 and the registry number is 52356454783589556107591165111051208512 Terminal H atoms not shown In 1982 Fuller and Keppert outlined a new method for analysing the structures and rearrangement pathways of three closo-boranes [B,H,]'- (n = 8 9 or 12). In this method every boron atom interacts with every other the strength of that interaction being (l/d") -(l/dY) and the total cluster bonding energy of the molecule being the sum of all such components. The coefficients x and y were set to 2 and 1 respectively by best fitting of the known structures of [B8H8I2- and [B9H9I2-.In a recent second paper'29 the same coefficients are used to predict optimized structures for all species [B,H,I2- for n =*5-12. In all cases where structures are known experimentally there is agreement with those predicted by this method and there is generally good agreement with the predictions of previous geometry-optimizing calculations (MNDO PRDDO). However a note advocating that the Fuller-Keppert approach be used with caution has also a~peared.'~' The criticisms are made that the method gives unrealistic relative energies within the series that it overestimates the lengths of B-B connectivities in small polyhedra and underestimates those in large ones that it overemphasizes the importance of radial versus tangential B-B bonding and that it leads to the unrealistic conclusion that relatively high-connected boron atoms are relatively more strongly bound within the cluster.The protonations of a variety of boranes and carbaboranes have been studied via MNDO calculations (and for 1,6-C2B4H6 uia ab initio MO calculations 3-21G basis set).I3' The site of localization of the HOMO of the substrate is that attacked this affording protonation of BBB triangular faces (e.g. in 1,12-C2BloH,2) of B-B edges (e.g. in &,HI') protonation resulting in a 3c-BH2 bond (e.g. in B2H6) or a 2c-BH bond (in [B4H4I2-) and protonation at carbon (generating a 2c C-H bond) in 1,5-C2B3H5 and 2-CB5H9. MNDO MO energies for closo-borane dianions and closo-carbaboranes have been linearly related to energy equations given by Stone's tensor surface harmonic (TSH) theory thereby lending support to the assumptions and utility of the TSH approach to cluster bonding.'32 The new hypho-species [B,H,PMe3]- has been prepared,'33 as its potassium salt by reaction of KB4H9 with PMe, and n.m.r.data have been interpreted in terms of a structure represented by the localized bonding description (50). This study I29 D. J. Fuller and D. L. Kepert Polyhedron 1983 2 749. 130 C. E. Housecroft and K. Wade Inorg. Chem. 1983 22 1391. 131 R. L. DeKock and C. P. Jasperse Inorg. Chem. 1983 22 3843. 132 P. Brint J. P. Cronin E. Seward and T. Whelan J. Chem. SOC.,Dalton Trans. 1983 975. I33 M. Shimoi and G. Kodama Inorg.Chern. 1983 22 1542. A. J. Welch prompted a thorough investigation of the reaction of B4H10 with phosphine in donor solvent; when molar equivalents of Me3P and B4H,0 react in THF at low tem- peratures Me3P.BH3 THF.B3H7 and [(THF),BH,]+[B,H,]-are mainly pro-d~ced,’~~ not Me3P.B3H7 and THFeBH,. The observed products are discussed in relation to cleavage mechanisms of B4Hlo. Stepwise addition of PMe3 to to form the belt-shaped B6Hlo.2PMe3 was described two years ago and now reaction of this with excess of phosphine has been re~0rted.l~~ Although complete separation of the reaction products has not been possible spectroscopic study suggests that the belt structure is cleaved to afford B2H4-2PMe3 B,H6.4PMe3 and two equivalents of B3H5 .3 PMe,.“B and 2H n.m.r. experiments have defined two relatively low-energy pathways for Lewis-base catalysed hydrogen exchange in XB5H8 molecules the energetically more favourable one involving scrambling of basal-terminal and bridge H atoms and the other involving exchange of H and migrating substituents (e.g. X = Me,Si) between basal and apical positions. It is argued that the latter pathway probably does not proceed via a simple 1,2-~hift.‘~~ The coupling of B5H9 with alkenes under mild conditions to afford good yields of 1-and 2-substituted alkenylpentab~ranesl~’ is catalysed by PdBr, whilst PtBr catalyses’38 the self-coupling of B,H9 to 1 :2’-( B5H8)2. Interestingly no evidence was found for the co-formation of either 1 1’-(B,H8) or 2:2’-(B,H,),.The lithium salt of the latter isomer has been assessed as an alternative precursor to [BsH8]- for polyhedral expansion syntheses.139 Reaction with B2H6 followed by acidification affords B,0H14 and more importantly n-B9H13 via the mechanism (suggested by isotopic enrichment experiments) of Scheme 2 i.e. bridge attachment of BH3 fol- lowed by polyhedral reduction and subsequent interaction of B5 and pendant B units. Interatomic distances in inter alia [B9H9I2- B&19 and C2B7H9 have been in relation to the non-degeneracy of the frontier orbitals of the parent borane uiz. [B,H,]’-. The ten-vertex thiaborane 6-SB9H1 is an unusual example of a polyhedral hydro- boration reagent and it has recently been shown that multiple hydroborations may be achieved with it.14’ Thus 6-SB9H, reacts with excess cis-hex-3-ene to afford 9-monohexyl 1,9-dihexyl and 1,3,9-trihexyl derivatives in multiple hydroboration reactions that appear to be reversible.Preliminary results indicate that 6-SB9H1 I34 M. Shimoi and G. Kodama Inorg. Chem. 1983 22 3300. 135 M. Kameda and G. Kodama Polyhedron 1983 2 413. ‘36 J. A. Heppert and D. F. Gaines Inorg. Chem. 1983 22 3155. 13’ T. Davan E. W. Cocoran jun. ahd L. G. Sneddon Organomefallics 1983 2 1493. 13* E. W. Corcoran jun. and L. G. Sneddon Inorg. Chem. 1983 22 182. ‘39 A. M. Barriola Acta Cient. Venez. 1983 34 25. 140 M. E. O’Neill and K. Wade Polyhedron 1983 2 963. 141 N. Canter C. G. Overberger and R. W. Rudolph Organometallics 1983 2 569. Boron 39 Reagents i MeLi; ii B,H,; iii H' Scheme 2 (Reproduced by permission from Acta Cient.Venez. 1983 34,25) reacts with polybutadiene to produce a cross-linked polymer. 6-SB9Hl and its selenium analogue reactI4* with alkyl isocyanides to form two isomeric adducts for which structures (5 1) and (52) are proposed. Whereas (5 1) is relatively stable (52) undergoes cage insertion of the ligand C atom to afford the nido-1 1-vertex thia- or selena-carbaborane (53). RN \ NR (51) (52) (53) Degradation-insertion reactions of BIOHI4 have been discussed by Base,143 and thus routes to a number of medium-sized aza- selena- and thia-boranes (including 6-SB9HI are summarized (Scheme 3). The crystal structure of 2-Br-6,9-(SMe2),- BloHl has been reported,I4 and although the molecular structure itself is relatively uninteresting (albeit the first example of optical isomerism in a decaborane deriva- tive) its solution is meritorious in that tetragonal twinning of orthorhombic lattices I42 A.Arafat G. D. Friesen and L. J. Todd Znorg. Chern. 1983 22 3721. I43 K. Base Collect. Czech. Chern. Comrnun. 1983 48 2593. V. Petricek 1. Cisarova and V. Subrtova Acta Crvstallogr. Sect. C 1983 39 1070. A. J. Welch 1 NaN02,THF 1. KHS0,.H20 2.conr. WlS04 1 conc. H250 \KH SO].H~O 0 BlQH14 6-SBpHI1 tI Il..Na2St03 2 dil HCl .THF\ 2.811. HCI SOIUl ;c n L 4-NBgHl3 9-L-6-NB9H12 6-NB9H13 Scheme 3 (Reproduced by permission from Collect. Czech. Chem. Commun.,1983 48 2593) was unravelled.Reaction with alkynes of the non-brominated species BloH ,,(SMe,) is a standard synthetic route to dicarbaboranes in which it has been proposed that BI0Hl2SMe2 (whole structure is unknown) is an important intermediate. It has recently been however that the unique 6,9-bridged phosphido-species ar~chno-[B,~H,~PPh~]-(54) may provide a structural analogue for BIoH,,SMe2. The only closo-borane dianion in the series [BnHnl2- (n = 6-12) for which neither a solid-state nor a limiting solution structure is known is [BIlHll]2- the only structural information available being that which relates to a derivative or to heteroborane analogues. This list has been recently supplemented by crystallographic and n.m.r. study14" of [B ,HlOSMe2]- shown to have the expected octadecahedral architecture (55) in which the SMe function is bound to B-4.1 2 3 8 9 I45 M. A. Beckett and J. D. Kennedy J. Chem. Soc. Chem. Commun. 1983 575. I46 E. H. Wong L. Prasad E. J. Gabe. and M. G. Gatter Inorg. Chem. 1983 22 1143. Boron 41 The subhalides of boron have been reviewed by Massey.14’ A re-e~amination’~~ of the thermal decomposition of [H30]2B10C110 has shed light on a previous anomaly in born subhalide chemistry viz. the IlB n.m.r. spectrum of ‘HB9Cls’ whose four resonances (one split by H) could not be reconciled with the expected tricapped trigonal prismatic structure. In reality ‘HB,Cl,’ is a mixture of HB9C18 H2B9C17 and BgC19. Also produced in the decomposition study are BloCllo BllClll and BI2Cll2 as well as the entire range of supraicosahedral subhalides B,Cl (n = 13-20).Unfortunately it has not yet proved possible to separate these. 7 Metallaboranes and Derivatives Deuterium labelling experiments have been used to study the (Ph3P),CoC1-activated hydrogenation of diphenylethyne by NaBH,. Typically after prior reaction in THF the mixture is acid hydrolysed and although the major source of the vinylic H atoms in the cis-and trans-stilbene formed is the BH4- ion a minor source must be the s01vent.I~~ The reaction presumably proceeds via formation of a Co-BH complex. Reductive hydrogenations of C02 and COS to (R,P),Co( q2-0,CH) and (R3P),Cu( q2-OSOH) respectively and of SCNPh to (R,P),Cu( q2-S2CNHPh) by q2-BH,) (R = Ph or cyclo-C6H1 have been in~estigated,’~’ (R3P)2C~( and novel q’-bonded terminal and bridging formate complexes result from addition of one equivalent of PPh3 to the C02-Ph3P system.Addition’” of excess phosphite to {(R0)3P}2Cu(q2-H3BC02Et) (56) (R = Me or Et) affords ultimately the ionic species [{(R0),P},Cu]+[H3BC02Et]-. Analysis of ‘H n.m.r. data for (56; R = Me) has allowed AG’ for the fluctionality (bridge- terminal hydrogen exchange) of {(MeO),P),Cu( q2-BH4) to be estimated as 4.3 kcal- mol-’. It is proposed that this value is less than that for (T-C~H~)~V(~~-BH,) because of the greater degree of covalency in the M-H-B bridge system of the latter.lS2 A Ta-H-B bridge exists in the bis(pyrazoly1)borate complex {H2B(3,5- Me,pz),}TaMe,Cl (57). Although H-1 1 was not located in a crystallographic study the stereochemistry at Ta and short Ta-B distance 2.897( 12) A are consistent with its presumed position and moreover i.r.and coupled ’’B n.m.r. spectra (the latter up to 110 “C) imply its existence and thermodynamic ~tabi1ity.l~~ A most unusual mode of BH co-ordination has been established in Co2( BH4)2{ Ph2P(CH2),PPh2) (58) structurally studied as its 0.5 C6H6 s01vate.I~~ All hydrogen atoms attached to boron were located and refined. The BH units are both tridentate and bridging (this work represents the first structurally proven example of bridging BH,) and the existence of three chemically different types of BH hydrogen atom is fully supported by i.r. spectroscopy. To distinguish bridging and multidentate A.G. Massey Adv. Inorg. Chem. Radiochem. 1983 26 1. I48 D. A. Saulys N. A. Kutz and J. A. Morrison Inorg. Chem. 1983 22 1821. I49 E. Steinberger M. Michman H.Schwarz and G. Hohne J. Organornetal. Chern. 1983 244 283. I so C. Bianchini C. A. Ghilardi A. Meli S. Midollini and A. Orlandini J. Organornetal. Chern. 1983,255 C27. Is’ J. C. Bommer and K. W. Morse Inorg. Chern. 1983 22 592. IS2 J. C. Bommer and K. W. Morse Inorg. Chirn. Acta 1983 74 25. IS3 D. L. Reger C. A. Swift and L. Lebioda J. Am. Chem. Soc. 1983 105 5343. IS4 D. G. Holah A. N. Hughes S. Maciaszek and V.R. Magnuson J. Chem. SOC. Chern. Commun. 1983 1308. A. J. Welch (57) (Reproduced by permission from J. Am. Chem. SOC.,1983 105 5343) (Reproduced from J.Chem. SOC.,Chem. Commun. 1983 1308) co-ordination of BH4 we shall in this year's Report adopt p for the former and V" for the latter. In {q-C5H3(SiMe3)2}2(THF)nM(BH4) (M = Sc n = 0; M = Y or Yb n = 1) the BH moiety is T2-co-ordinated whereas in analogues of larger metals (M = La Pr Nd or Sm n = 1) it is q3-bound. IlB N.m.r. spectroscopy reveals that for the Sc complex only the BH4 co-ordination is relatively static.'55 Since this is the only I55 M. F. Lappert A Singh J. L. Atwood and W. E. Hunter J. Chem. SOC.,Chem. Commun. 1983 206. Boron 43 member of the series that is not solvated it is possible that in those cases where fluctionality (bridge and terminal H exchange) occurs it does so via a 7'-bonded intermediate whose relative electron deficiency is mitigated by co-ordinated THF.Anionic tetrakis(tetrahydrob0rate) complexes of Gd Tb Dy Ho Er Tm Yb and Lu have been reported,156 and i.r. study suggests that the first two of these contain q3-BH4 and p-(q2)*-BH4functions whereas for the heavier elements simple 773 -co-ordination occurs. An accurate low-temperature neutron diffraction studyI5' of H~(T~-BH~)~ (59) affords parameters Hf-Hb 2.130(9) B-Hb 1.235( lo) and B-HH 1.150(9) A; HfHB 80.6(6)".X-Ray studies of M(q3-BH3Me) (M = Zr Np U or Th) have also been rep~rted;'~~ not surprisingly only for the zirconium analogue could H atoms be refined yielding (Zr-H) 2.06A (B-H) 1.14A. The Zr and Np species are isomorphous and the U and Th compounds are separately nearly isomorphous.1.r. and n.m.r. data (reported for all except the Np analogue) are in full accord with v3-co-ordination. (Reproduced by permission from Inorg. Chern. 1983 22 1081) Full details have now been p~blisedl~~ of the structure of [NaBHMe,],-Et,O which has a very distorted pseudo-cubane Na4H4 core ((H-a-H) 2.73 A (Na-m-Na) 3.611 A) with closest Na-H distances between 2.25 and 2.42 A. (B-H) is 1.20(7) A. Grimes has reviewed the role of transition metals in borane and carbaborane clusters with particular emphasis on the cluster stabilization that the metal affords and metal-promoted coupling fusion and intramolecular hydrogen transfer reac- tions. I6O The overall result of reaction of H20s3(CO),o with BH3NEt3 and 0.5 B2H6 is insertion of a boron atom into an Os-CO bond to yield the carbonyl borylidyne I56 V.D. Makhaev A. P. Borisov B. P.Tarasov and K. N. Semenenko Zh. Neorg. Khim. 1983 28 340. 157 R. W. Broach 1.4. Chuang T. J. Marks and J. M. Williams Inorg. Chem. 1983 22 1081. 158 R. Shimomoto E. Camp N. M. Edelstein D. H. Templeton and A. Zalkin Inorg. Chem. 1983,22,2351. 159 N. A. Bell H. M. M. Shearer and C. B. Spencer Acta Crystallogr. Sect. C 1983 39 694. 160 R. N. Grimes Acc. Chem. Rex 1983 16 22. A. J. Welch species (60) in which the BCO unit face bridges the metal triangle.I6' A mechanism is proposed in which it is the borane-amine adduct that affords the BH unit that is the net addition to the metal substrate. 0 22 13 (Reproduced by permission from J.Am. Chem. SOC.,1983 105 5923) Preliminary details of the ferraborane HFe,(CO) 12BH2 were reported last year. Full structural information and a thorough discussion of this cluster have now been published.162The application of simple electron counting procedures to this molecule is ambiguous but the narrow (1 14") dihedral angle between Fe3 triangles suggests classification as an arachno Fe cluster with interstitial boron atom (or in Mingos- Lauher terms a 62 electron saturated cluster). This view is supported by the results of Fenske-Hall MO calculations which have also rationalized the observed orienta- tion of the BH2 fragment and which suggest that deprotonation of the molecule would occur by loss of a boron-bonded H. Fenske-Hall calculations have also been employed'63 to aid assignment of the UVPE spectrum of ( q-C,H,) (C0)2Fe(B2H,) (61).Analogy is made between the [B2H5]-ligand of (61) and the C2H ligand of Fe(C0)4(C2H,); [B2H5]- is regarded as q2-[B2H4I2- protonated on the opposite side of the B-B bond to the metal atom. EHMO calculations are then used to analogize higher boranes with appropriate r-bonded hydrocarbons attention being focused on the role of bridging H atoms of the former in reorientation of ligand r-orbitals. The important point is made however that borane ligands are generally less good at stabilizing low oxidation state metal centres because of their limited T-acceptor capability. S. G. Shore D.-Y. Jan L.-Y. Hsu and W.-L. Hsu J. Am. Chem. SOC. 1983 105 5923. '62 T. P. Fehlner C.E. Housecroft W. R. Scheidt and K. S. Wong Organometallics 1983 2 825. R. L. DeKock P. Deshmukh T. P. Fehlner C. E. Housecroft J. S. Plotkin and S. G. Shore J. Am. Chem. SOC.,1983 105 815. Boron 45 The complement to this of course is that boranes should be quite appropriate ligands for high oxidation state metals and Greenwood and colleagues have pre- viously utilized this feature to prepare metallaboranes with formal valencies as high as +5. In 1983 the scope of the synthetic program of the Leeds group has been widened to include the first osmaboranes. Thus Os(CO)(Cl)( H)( PPh,) reacts with [B3H8]- and [B,H,]- to afford164 (HOsB,H,)(CO)(PPh,) (62) and (OsB,H,)(CO)- (PPh3)2 (63) for which the structures shown are proposed on spectroscopic grounds.[B,H,]-also reacts with IrCl( PPh,) to yield (H21rB,H8)(PPh,), structurally similar to (62). Mild thermolysis (100 "C C,Cl,) of (63) affords (OsB,H,)(CO)(PPh,) for which the nido structure (64) is suggested. An osmaborane intermediate is impli- cated16 in the edge-fusion of nido-[B,H,,]-polyhedra to yield anti-[B,,H21]- under CH2CI2 reflux in the presence of [Os(CO),CI],. (64) (Reproduced by permission from J. Organometal. Chem. 1983 249 11) The same group of workers has additionally synthesized heterobimetallic metal- laboranes starting with a nido-metallaborane and with it performing analogous reactions to those of nido-boranes. Thus 6-( Ph,P)-6-( Ph2P-2'- C6H4)-6-H-nido-6-IrB,H12-j (65) (analogue of B,0H,4) may be treated166 with KH and then cis-PtCl,(PMe,) to yield 7,7-( Me,P),-9-( Ph,P)-9-( Ph,P-2'- C6H4)-9-H-nido-7,9-PIrB9H10-~(66).Similarly (63) with NaH then cis-PtC12(PhMe2P) yields167 (Ph3P),(CO)0s(PhMe2P)ClHPtB5H7(67; p-H not directly located) and here (63) is a surrogate for B&il,. Products (66) and (67) with different 164 J. Bould N. N. Greenwood and J. D. Kennedy J. Organometal. Chem. 1983 249 11. 165 J. Bould N. N. Greenwood and J. D. Kennedy Polyhedron 1983 2 1401. 166 J. Bould J. E. Crook N. N. Greenwood J. D. Kennedy and W. S. McDonald J. Chem. Soc. Chern. Commun. 1983 949. 167 J. Bould J. E. Crook N. N. Greenwood and J. D. Kennedy J. Chem. Soc. Chem. Commun. 1983,951. A. J. Welch (65) (Reproduced from J. Chem. SOC.,Chem. Commun. 983 949) metal atoms connected via a boron cage have been termed 'B-frame compounds' and their synthesis and subsequent structural elucidation sheds possible light on the mechanisms of polyhedral expansion reactions ;for example on following the position of the ortho-phenylene function in the synthesis of (66) from (65) it is evident that polyhedral isomerization has occurred.From the analogous reaction of BIDHI4 one could not easily establish this (although of course these 'analogous' reactions may follow different paths). (67) (Reproduced from J. Chem. Soc. Chem. Commun. 1983 951) The structure of the macropolyhedral 17-vertex platinaborane (PhMe,P),- Pt3B14H16 has been determined,'68 and three views of it (whole molecule minus H atoms additionally minus phosphine ligands and additionally minus metals) are given in (68).B(1I) does not have a terminal H and bridging H atoms are ascribed M. A. Beckett J. E. Crook N. N. Greenwood and J. D. Kennedy J. Chem. SOC.,Chem. Commun. 1983 1228. Boron 47 to B(4’)-B(5’) B(4’)-B(9‘) and the Pt(7,6)B(8)B(9)Pt( 10,8‘) sequence. It is sug- gested that the macropolyhedron be viewed as nido 11-vertex (unprimed atoms) and arachno 9-vertex (primed atoms) polyhedra fused about their common PtBPt face. (68) (Reproduced from J. Chem. SOC.,Chem. Commun. 1983 1228) 8 Carbaboranes and Carbametallaboranes Onak and co-workers have accurately remeasured ‘J(BH) for the entire range of known closo-carbaboranes C2Bn H2+, (n = 3-1 0) and have established an empirical correlation between J the appropriate ‘umbrella’ angle (the average interior angle of a cone in the polyhedral surface whose apex is the boron atom clearly related to the s-character of the exopolyhedral B-H bond) and the number of adjacent cage carbon atoms.’69 Good agreement occurs for all species except 1,7-C2B,H (probably fluctional in solution) and 1,6-C2BsHlo (incomplete data and assignments).The utility of this method is demonstrated in that it has facilitated complete assignment of the chemical shifts in 2,3-C2B9H1 1. A re-examination of the gas-phase pyrolysis of 1,5-C2B3H5 has verified the pre- viously reported formation of the B-B linked dimer 2:2’-( 1,5-C2B3H4)2 and trimer 2:2’,3‘:2”-(1,5-C2B3H4)( 1’,5’-C2B3H3)( 1”,5”-C2B3H,) and has also identified the new species 1:2’-( 1,5-C2B3H4)2 (69) 2:2’,1’:2”-( 1,5-C2B3H4)( 1’,5’-C2B3H3)- ( 1”-5”-C2B3H4) (70) 2:2’,3’ 1”-(1,5-C2B3H,)( 1’,5’-C2B3H3)( 1”,5”-C2B3H4) (71) and 1,2,8,1 0-C4B7HI (72) for which the structures shown are proposed on spectroscopic ground^."^ (69)-(71) all contain B-C intercage linkages and (70) is especially I69 W.Jarvis Z. J. Abdou and T. Onak Polyhedron 1983 2 1067. R.J. Astheirner and L. G. Sneddon Inorg. Chem. 1983 22 1928. A. J. Welch (71) (72) (Reproduced by permission from Znorg. Chem. 1983 22 1928) interesting in that the linkages are perpendicular. The mechanism of formation of (72) is unclear. Pyrolysis of 1,6-C2B4H6 affords only polymerization but co-ther- molysis of it and 1,5-C2B3H5 yields 2’:2-( 1’,5’-C2B3H4)( 1,6-C2B4H5) in improved yields compared with its previous photochemical production.It had previously been established that reaction of (q-C,H,)Co(CO) with an isomeric mixture of the linked carbaborane (2,4-C2B5H6)2 affords six isomeric carbametallaboranes and now structural study of one of these (73) reveals it to be Le. 3’:2(2‘,4‘-C,B,H,)( 1,8-{ q-C,H,),-1,8,5,6-Co2C2B5H6),a tricapped (B + 2C) trigonal-prismatic carbadicobaltaborane linked to the pentagonal-bipyramidal car- baborane via a B(2)-B(3’) bond.”’ Q (Reproduced by permission from Inorg. Chem. 1983 22 1765) A new route to the B-B-linked bis(carbaborane) (Me2C2B10H9)2 has been repor- ted oxidation of 1,2-Me2-1 ,2-C2B10HI0 with T1(02CCF3)2 in the presence of 10% Pd(OAc) affording the product in 35% ~ie1d.I’~ A reasonable (10%) yield of ~so-C~B,~H~~ is produced by thermolysis (80 “C,benzene or toluene) of nido-7,8-C2B9H13.Analyses of the mass spectrum and of the proton and IlB n.m.r.spectra R. P. Micciche J. S. Plotkin and L. G. Sneddon Znorg. Chern. 1983 22 1765. 172 A. Ya. Usyatinskii A. D. Ryabov T. M. Shcherbina V. I. Bregadze and N. N. Godovikov Izu. Akad. Nauk SSSR Ser. Khim. 1983 1637. Boron 49 of iso-C4BaHl confirm that it comprises a closed 1,2-C2BI0H1 icosahedron linked to a nido-5’,6’-C2BaH1 octadecahedral fragment by a B(3)-B(8’) bond.173 Arene carbametallaboranes have been the subject of recent research activity since their initial synthesis in 1981. The major product of the co-condensation of iron atoms toluene and nido-2,3 -Et2-2,3-C2B4H6 is174 the closo pentagonal-bipyramidal species 1-(q6-PhMe)-2,3-Et2-l ,2,3-FeC2B4H4 (74) (for which a crystallographic study is reported) although mass spectrometric evidence for iron-C4B7 and -C4Bg complexes is also given.Alternatively 1-( q6-CaHlo)-2-3-Et2-1,2,3-FeC2B4H4(75) (produced’75 by reaction of [C8Hs12- FeCl, and [Et2C2B4H5]-) reacts with arene over AlC13 to yield aAalogues of (74) (arene = C6H6 1,3,5-Me&H3 or C6Me6) all species being characterized by i.r. and multinuclear n.m.r. spectroscopies mass spectrometry and X-ray diff ra~ti0n.l~~ Co-produced with (75) are rather surpris- ingly its q6-C6H6 analogue and (Cl6HIa)Fe( ; spectroscopic data are Et2C2B4H4) given for the latter but there is no structural a~signment.’~’ (75) characterized by an X-ray study of its 2,3-Me2 analogue also reacts’76 with tetramethylethyl- enediamine to abstract the unique equatorial boron atom and afford (q6-c8H10 Fe( Et2C2 B3 H5 -If VCl replaces FeC1 in the reaction that produces (75) the result17’ is the q8-bonded cyclo-octatetraenyl species 1-(q8-CaHa)-2,3-Et2-1,2,3-VC2B4H4 (76) a unique compound in that it is the first example of q8-bound CsHa to a first transition series element other than Ti.The species is electron deficient in that (assuming a formal [CgH,]’- exopolyhedral ligand) it either has 2n + 2 cluster bonding electrons (n = 7) and a 17e metal centre,. or only 2n + I cluster electrons at variance with the predictions of the Polyhedral Skeletal Electron Pair (PSEP) theory and an (76) (Reproduced by permission from J.Am. Chem. Soc. 1983 105 2079) I73 2. Janousek J. Plesek B. Stibr and S. Hermanek Collect. Czech. Chem. Commun. 1983 48 228. I74 R. P. Micciche and L. G. Sneddon Organometallics 1983 2 674. I75 R. B. Maynard R. G. Swisher and R. N. Grimes Organometallics 1983 2 509. I76 R. G. Swisher E. Sinn and R. N. Grimes Organometallics 1983 2 506. R. G. Swisher E. Sinn G. A. Brewer and R. N. Grimes J. Am. Chem. SOC.,1983 105 2079. A. J. Welch electronically saturated vanadium atom. A preference is expressed for the former; see also the discussion of compounds (81) (90) and (91). In attempting to.extend the chemistry of closo-5-C1-C2B5H6 (some details of which were reported last year) to the bromo analogue Onak and Fuller have found178 that Me3N.5-Br-C2B5H undergoes halogen exchange with CH2C12 affording 5-C1-C2B5H6 and [Me3NCH2Cl]Br presumably via a [5-Me3N-C2B5H,]+ intermediate.The eight-vertex carbacobaltaborane 3-(77-C5H5)-1,2-Me2-3,1,2-CoC2B5HS has a dodecahedra1 cage geometry with the metal atom (five-connected with respect to the cluster) and carbon atoms (four-connected) constituting one face. 179 Three closo ten-vertex (bicapped square antiprismatic) monocarbon carbametal- laboranes have been separately reported. In [2-(77-C5H5)-2, l-CoCB,H,]- struc-turally studiedlBO as its NMe,+ salt and in p-1,2-(MeC02)-2-H-2,10-(PPh3)2-1 ,2-CIrB,H (77) (formed,lB1 in <I% yield by refluxing [BloH,o]2- with trans-Ir(CO)Cl(PPh,) in MeOH) the metal atoms are five-connected and adjacent to a carbon cap This contrasts with I ,2,2-( PPh3)3-2-H-2,10-IrCB8H8(78) in which the heteroatoms are separated although (77) and (78) share the common feature that it is the four-connected boron atom to which the PPh3 ligand is bound.(78) is one (77) Terminal H atoms on boron atoms and on Ir(2) not shown (Reproduced from J. Chem. SOC.,Chem. Commun. 1983 83) 178 K. Fuller and T. Onak J. Organometal. Chem. 1983 246 C6. 179 G. J. Zimmerman and L. G. Sneddon AC~Q Crystallogr. Sect. C 1983 39 856. I80 K. A. Solntsev L. A. Butman I. Yu. Kuznetsov N. T. Kuznetsov B. Stibr 2.Janousek and K. Base Koord. Khim. 1983 9 993. J. E. Crook N. N. Greenwood J.D. Kennedy and W. S. McDonald J. Chem. SOC.,Chem. Commwn. 1983 83. Boron 51 of several products of the reactions between [CBgH13]- and IrCl(PPh,), and a possible mechanism is discussed.Ig2. The B-H-B functions of nido-5,6-C2BgH12are sufficiently electrophilic to react with Pt2(p-C,H12) (PEt,) to yieldlg3 9-H-9,9-(Et3P)2-p,0,1 -H-7,8,9-C2PtB8Hlo (79) a nido-icosahedral formally PtIV species. Upon thermolysis (79) evolves one molar equivalent to H2 in being transformed into 9-H-9,10-( Et3P),-7,8,9-C2PtB8H9 (80) (79) In (79) there is a p-H between B(10)and B(11) (Reproduced from J. Chem. Soc. Dalton Trans. 1983 2063) which could be considered a very distorted octadecahedral cluster with a formally +2 oxidation state metal atom since one phosphine ligand has transferred from Pt(9) to B( 10).Nido-5,6-C2B8H12 also reacts with (T-C~H,)~N~ to affordlg4 the nido-carbanickellaborane(8 1) crystallographically studied as thus and in derivative form (82) in which the remaining bridge hydrogen atom is replaced by the isolobal AuPPh fragment. (q-CgH5)2Cr is apparently more reactive towards the same nido- carbaborane since the only product isolated from their reaction is the dimetal species (83) [presumably formed via an intermediate similar to (Sl)]. This overall set of reactions is summarized in Scheme (4). (8 l) too was identified crystallographically and contains the shortest metal-metal distance 2.272(2) A yet recorded in a heteroborane cluster a feature that has been reproduced by EHMO calculations.The electron count in (8 1) is interesting in that the polyhedron is electron deficient (in the PSEP sense) by 6e if one requires that the (q-C,H,)Cr fragment is a le acceptor thereby satisfying the 18e rule. However if the valence electron count is only 15 (‘fZR’ orbitals singly occupied) then the cluster is precise (again in PSEP terminology) and the deficiency resides on the metals. A similar situation has arisen previously [compound (76)] and is met later in this section [compounds (90) and (91)]. In simple terms the ‘multiple’ Cr-Cr bond in (81) is the result of bonding interactions between these sets of adjacent singly occupied metal atomic orbitals. N. W. Alcock J. G. Taylor and M. G. H. Wallbridge J. Chem. Soc. Chem. Cornmun.1983 1168. I83 G. K. Baker M. Green F. G. A. Stone W. C. Wolsey and A. J. Welch J. Chem. Soc. Dalton Trans. 1983 2063. I84 G. K. Barker N. R. Godfrey M. Green H. E. Parge F. G. A. Stone and A. J. Welch J. Chem. Soc. Chem. Cornmun. 1983 277. A. J. Welch Reagents i (~pc~H~)~Ni; ii MeAuPPh,; iii (~pC~H~),cr Scheme 4 (Reproduced from J. Chem. Soc Chem. Commun. 1983 277) 1,2-C2BloH has been reported revealing The crystal structure of p8,8f-SCH2S-( the presence of two conformers in the solid state (2= 4 in space group P21) differing in the magnitude of the torsion angle about one of the S-C bonds.I8’ The icosahedral carbaborane cages are quite normal ((C-C) 1.598A (C-B) 1.672 A (B-B) 1.755 A) and the mean B-S (exopolyhedral) distance is 1.871 A.Anionic icosahedral bis(1igand)carbarhodaboranes with 3,l ,2-RhC2 2,l ,7-RhC2 and 2,1,1 2-RhC2 heteroatom substitution patterns have been produced by proton abstraction from their neutral hydride analogues,186,* and the bis(tripheny1phos- phine) members of the first two types structurally characterized. The conformations adopted by the (Ph,P),Rh’ fragments resemble those previously established for (R3P)2Pt11fragments although the rhodium species do not display the slipping distortions that characterize (especially the 3 I ,2-PtC2) platinum compounds. In C. Novak V. Subrtova A. Linek and J. Hasek Acta Crystallogr. Sect. C 1983 39 1393. I86 J. A. Walker C. B. Knobler and M. F. Hawthorne J. Am. Chem. SOC.,1983 105 3368. * There appears to be a type-setting error in the paper that could lead to confusion.Presumably the 2nd line of the 2nd paragraph should read ‘3,1,2-RhC2BPH (I a)’ only. Boron 53 solution there is hindered rotation about the metal-cage axis. These bisphosphine species are readily converted into phosphine/carbonyl complexes [(Ph,P)-(CO)RhC2B9H11]-,and it is argued i? a following comm~nication'~~ that the formal description (Ph3P)(C2B9HI,)Rh2-C=0 might lead to [3 + 21 cycloaddition reac- tions with 1,3-dipolar substrates. This does indeed happen cycloadducts being obtained by reaction with benzhydroxamic acid chloride or its rn-fluoro-derivative ; a crystal structure of the anion (84)obtained from the latter acid chloride and the 2,1,7-RhC2 cage shows bond lengths consistent with C=N and (exocyclic) C=O double bonds.TheCe cycloadducts readily lose C02 (and benzonitrile or rn-fluorobenzonitrile) on warming and the possibility of using this strategy to decar- bonylate metal complexes under relatively mild conditions is discussed and one example given. This is clearly an important piece of transition-metal chemistry with implications outwith the specific area of boron clusters. (Reproduced by permission from J. Am. Chem. Soc. 1983 105 3370) 3,3-( Ph3P)2-3-H-3,1 ,2-RhC2B9H1 is also the precursor for [HPPhJ-[3-Ph3P-3,3-Br2-3,1,2-RhC2B9H, isolated as the tight ion pair shown in (85) by reaction188 of the neutral carbarhodaborane with BBr,. Nim.r. data suggest that two rotational conformers of the anion exist in solution that displayed by the X-ray study (asymmetric) and a symmetric alternative (which predominates at high tem- peratures) in which the phosphorus atom lies on the cage mirror plane cisoidal to C( 1) and C(2).Ligand interchange [phosphine for H(8) i.e. formation of Ni-H and B(8)-P bonds from Ni-P and B(8)-H bonds] as a consequence of heating 3,3-(Ph,P),- 3,1,2-NiC2B9H1 has been known for some years but now a re-investigati~n'~~ of the system (various phosphines various isomers) has established that it only occurs for triarylphosphine complexes and only for the 3,l ,2-NiC2 isomer. A mechanism is proposed that involves dissociative loss of free phosphine which subsequently attacks B(8). As a complement to these studies ligand dissociation and substitution reactions of the 3,3-( PR3) species and reactivity studies of the 3,8-( PR3)2 species are also reported.The new complex (86) was prepared by a number of routes and 187 J. A. Walker C. B. Knobler and M. F. Hawthorne J. Am. Chem. SOC. 1983 105 3370. 188 L. Zheng R. T. Baker C. B. Knobler J. A. Walker and M. F. Hawthorne Inorg. Chem. 1983,22 3350. I89 R. E. King 111 S. B. Miller C. B. Knobler and M. F. Hawthorne Inorg. Chem. 1983 22 3548. A. J. Welch B ? eI II (85) (Reproduced by permission from Inorg. Chem. 1983 22 3350) (86) (Reproduced by permission from Znorg. Chem. 1983 22 3548) has been studied crystallographically. The two icosahedral cages are linked by a Ni-Ni bond which is doubly bridged by carbonyls.Two quite different further examples of joined carbarhodaborane icosahedra have been reported by the same group. Reaction of FU-iCl(PPh,) with nido-B10C12CNH3 which is and base affords [2,2-(PPh3)2-2-H-1-NH2-2,1-RhCB,oH,o]-transformed in hot methanol into the dimeric anion (87) structurally studied as its [Bu,N]+ ~a1t.I~' In (87) there are three links between the icosahedra one Rh-H-Rh' I90 .I.A. Walker C. A. O'Con L. Zheng C. B. Knobler and M. F. Hawthorne J. Chern. SOC.,Chem. Commun. 1983 803. Boron 55 (87) (Reproduced from J. Chem. SOC.,Chem. Commun. 1983 803) (Reproduced by permission from Angew. Chem. 1983 95 738) and two Rh-NH,-Cl’. The Rh-Rh distance is 2.998( 1) A There are four connections between the icosahedra of [(Et3P)RhC2B9HI1],(88) uiz.a direct Cl-C1’ bond a direct Rh(3)-Rh(3’) bond 2.725( 1) A and two three-centre Rh(3)-H(4‘)-B(4’) (and complement) bonds.’” (88) is produced in moderate yield by the reaction between (v4-C8HI2)Rh(PEt3)C1 and the caesium salt of the bis-( nidu-carbaborane) [C2B9H1 1]22- in which the Cl-CI’ link already exists. P.E. Behnken C. B. Knobler. and M. F. Hawthorne Angew. Chem. 1983 95 738. A. J. Welch The (known) bis(carbaborane) complex [Fe(C2B9H1 has been synthesized electrochemically’92 using nido-[C2B9H 12]-in NaBr-DMSO and an iron electrode. Its neutral platinum analogue (previously unknown to this reporter although the corresponding NilV and PdIV species are well documented) is afforded by treatment of nido-C2B9H, with chloroplatinic acid in isopropyl Volkov Dvurechen- skaya and co-workers have published two further paper^'^^,'^^ on multiply linked carbacobaltaborane polyhedra [(C2B9HI l){Co( C2B8H 10)}nC~C2B9H to complement the existing literature We complete this section by discussing two papers concerned with supraicosahe- dral carbametallaboranes i.e.the cluster is or is a fragment of a closed polyhedron of more than 12vertices. It has been impossible to synthesize such species by solution direct insertion using nucleophilic nickel-group fragments but now the higher reactivity of the Co(PEt,) fragment has been utilized196 to afford the closed 13-vertex complex (89) from direct insertion into 1-Me-1,2-C2B10H In addition to the polyhedral metal atom co(4) (which occupies the docosahedral vertex of highest connectivity) (89) contains an exopolyhedral Co( PEt,) unit bonded to the cluster by H-bridged Co-Co and Co(2)-B(7) bonds.(89) (Reproduced from J. Chem. SOC.,Chem. Commun. 1983 137) I92 V. L. Shirokii A. A. Erdman Z. P. Zubreichuk N. A. Maier and Yu. A. Ol’dekop Zh. Obshch. Khim. 1983 53 951. I93 E. A. Chernyshev L. K. Knyazeva Z. V. Belyakova A. V. Kisin N. I. Kirillova A. 1. Gusev and N. V. Alekseev Zh. Obshch. Khim. 1983 53 1433. I94 S. Ya. Dvurechenskaya V. V. Volkov I. I. Gorbacheva and N. D. Krivosheeva Izv. Sib. Otd. Akad. Nauk SSSR Ser. Khim. Nauk 1983 74. I95 V. V. Volkov and V. N. Ikorskii Izv. Akad. Nauk SSSR Ser. Khim. 1983 252. I96 G. K. Barker M. P. Garcia M. Green F.G. A. Stone and A. J. Welch J. Chem. SOC. Chem. Commun. 1983. 137. Boron 57 Grimes and colleagues have previously synthesized open supraicosahedral car- bametallaboranes from the reactions of relatively electron-rich metals (Fe Co Ni) with &C4BsHs or its dianion (R = H or alkyl). As a complement to such studies these workers have now examined197 the behaviour of the relatively electron-poor ( q-CSHs)Cr fragment towards the four-carbon carbaborane R = Et. From reaction (CrC1,-C5H5-[Et4C4BaH8I*-) and work-up four species are identified two isomers of (~-C,H,)CrEt4C,BaH8 and two isomers of (7-C5HS)CrEt4C4B7H7. One of each pair (90) and (9 1) respectively have been characterised crystallographically. It is believed that (9 1) originates from metal reaction with a pre-formed C4B7 cluster and that the second CrC4B7 species (not studied crystallographically) is a degradation product of (90).(90) (Reproduced by permission from Inorg. Chem. 1983 22 873) (90) has an irregular open cage structure and (91) is also open but possesses an approximate molecular mirror plane. As previously discussed for (8 1) compounds (90) and (91) apparently violate PSEP theory if one necessarily assigns 18e configur- ations to the metal atoms but become reasonable in PSEP terms (2n + 4 framework electrons nido geometries as observed crystallographically) if electron deficiency -in this case 15e configurations only-of the metal centre is argued. Other similar examples involving transition metals from the left of the periodic table are known in the literature.9 Exopolyhedral Chemistry of Boranes and Carbaboranes Irradiation of ethyldiazoacetate-1 ,2-C2BloHI2 in C,F affords all four possible isomers of B-CH2C(0)OEt(C2BloHI through insertion of the carbene function CHC(0)OEt into B-H bonds of the ~arbab0rane.I~' Teixidor and have synthesized ligands containing either two cfoso-C2BloH, or two nido-C2B,Hg cages linked by the sulphur-containing chains S-S I97 R. B. Maynard Z.-T. Wang E. Sinn and R. N. Grimes Inorg. Chem. 1982 22 873. 198 G.-X. Zheng and M. Jones jm. J. Am. Chern. SOC.,1983 105 6487. 199 F. Teixidor and R. W. Rudolph J. Organometal. Chem. 1983 241 301. A. J. Welch or SCH2CH2S and SCH2S or SCH2CH2S respectively with the cage carbon atoms bound to the exopolyhedral sulphur atoms.When however cages were bridged by 1,2-( SCH2),C6H4 a polymeric product of uncertain order was obtained. Carbaborane cages exo to cyclic or polymeric phosphazenes were reported by Allcock and co-workers in 1980 and 1981 but such species do not afford metal derivatives presumably because of the proximity of the phosphazene to the open face of the nido polyhedron produced by base degradation. If however a CH spacer is inserted between P and cage C the desired products are attainable. Thus (92) affords (93) which appears to be protonated at the ring N opposite to the unique P [thus (93) is strictly a phosphazane] and via single or double deprotonations (93) serves as a source of q5-bonded carbaborane ligand (with exopolyhedral cyclic phosphazene) to suitable metal fragments.Alternatively prior pyrolysis of (93) affords highly polymeric derivatives analogous to those reported earlier but now with spacers and these too can be used to generate carbametallaboranes.200 I II Cl-PQ ,p-Cl c1/ \cl (92) (93) Tetrahedral dichlorocobalt complexes whose co-ordination spheres are ,completed by either two P(Ph2)C2B,,H, ligands or one P,P'-bidentate XzPC2BloHloPYZ ligand (X = Me2N Y = Z = Ph) have been synthesized:" the C2B,o fragment being 1,2-C2Blo in both cases. The same chelate ligand (with variations X = Ph Y = Z = Ph NMe, or F; X = Ph Y = NMe, Z = F; X = NMe, Y = Z = C,F,; X = NMe, Y = NMez Z = F) has also been utilized to afford a range of PtCl,(chelate) complexes.202 With RAX (R = Me or Ph A = P or As X = C1 or I) 1,2-(CH2MgBr),-1,2- C2B10H10undergoes exopolyhedral cyclization to yield P~,~-{CH,( R)ACHz}-1,2-C2B10HI0,from which A-bonded M(CO) (M = Cr Mo or W) derivatives are readily ~ynthesized.~'~ Rhodiumzo4 and platinum and palladium205 yomplexes have been described in which the metal is part of an exopolyhedral MB*C*CP ring (asterisked atoms are polyhedral) and which are similar to rhenium and manganese species reported in the past two years.In [B,oHlo]2- there exist two chemically different H atoms. It has been proposed that c~~-P~(PP~~)~(B~~H,~), formed by reaction between cis-Pt(PPh3),12 and 200 €3. R. Allcock A. G. Scopelianos R. R. Whittle and N. M. Tollefson J. Am.Chem. Soc. 1983 105 1316. 20 1 J. G. Contreras J. P. Pena and L. M. Silva-Trivino Bol. SOC.Chil. Quim. 1983 28 3. 202 W. E. Hill B. G. Rackley and L. M. Silva-Trivino Inorg. Chim. Acta 1983 75 51. 203 L. I. Zakharkin M. G. Meiramov V. A. Antonovich A. V. Kasantsev A. I. Yanovskii and Yu. T. Struchkov Zh. Obshch. Khirn. 1983 53 90. 204 V. N. Kalinin A. V. Usatov and L. I. Zakharkin Zh. Obshch. Khim. 1983 53 945. 205 V. N. Kalinin A. V. Usatov and L. I. Zakharkin J. Organometa!. Chern. 1983 254 127. Boron 59 (M+)2[B,oHloJ2-(M = K or Ag) exists as two dimers which differ in respect of the H atoms involved in Pt-H-B bridge bonds.206 [BloHlo]2- has also been reported to enter into inner-sphere co-ordination displacing amine ligands by thermolysis with Co and Cr.207 9-Hg Derivatives of C2B10H12 have been the subject of recent studies since such species are useful synthetic reagents because of the relative weakness of the B-Hg bond.Thus 9-Hg-( 1,2-C2B10H1 1)2 has been synthesized208 by mercuration of 9-1, (02CCF3)2Tl-1,2-C2BloH1and it is reported that thermolysis of 9-Hg-( 1,2- C2BIoHll),or 9-Hg-( 1,7-C2BI0Hll) cleaves the Hg-B bond to give the appropriate carbaborane B,B’-bis( carbaboranyl) and various oligocarbab~ranes.~~~ Mercur-ation of carbaboranes also affords an additional n.m.r.-active nucleus.210 Lithium derivatives of closo-carbaboranes are also of synthetic utility via classic coupling reactions eliminating LiX(X = halide). Thus 1-R-2-Li-C2BloHlo (R= Ph and I,7-Li2-C2B,,Hlo react with ( T-CIP~)C~(CO)~ or Me) 1,2-Li2-C2BIOH10 to yield the appropriate ( q-carbaboranylbenzene)Cr(CO) complexes,21 and carboranyl lanthanide complexes of several different stoicheiometries have been similarly prepared2 using lanthanide halides ; from certain of these trimethylsilylcar- baboranes and carbaboranyl ketones may be further derived.213 Alternatively car- baboranyl lanthanides are afforded by treatment of mercury carbaboranes with lanthanide metal/ Hg 206 Yu.L. Gaft Yu. A. Ustynyuk A. A. Borisenko and N. T. Kuznetsov Zh. Neorg. Khim. 1983,28 2234. 207 Yu. N. Shevchenko N. I. Yashina K. B. Yatsimirskii R. A. Svitsyn and N. V. Egorova Zh. Neorg. Khim. 1983 28 391. 208 V. I. Bregadze A. Ya. Usyatinskii and N.N. Godovikov Izu. Akad. Nauk SSSR Ser. Khim. 1983,1903. 209 L. I. Zakharkin and 1. V. Pisareva Izv. Akad. Nauk SSSR Ser. Khim. 1983 1158. 210 Yu. K. Grishin V. A. Roznyatovskii Yu. A. Ustynyuk V. Ts. Kampel and V. I. Bregadze Vesrn. Mosk. Univ. Ser. 2 Khim. 1982 23 488. 21 I L. I Zakharkin and G. G. Zhigareva Zh. Obshch. Khim. 1983 53 953. 212 V. I. Bregadze N. A. Koval’chuk N. N. Godovikov G. 2. Suleimanov and I. P. Beletskaya J. Organornerd. Chem. 1983 241 C13. 213 G. Z. Suleimanov V. I. Bregadze N. A. Koval’chuk Kh. S. Khalilov and I. P. Beletskaya J. Organomefal. Chem. 1983 255 C5. 214 G. 2.Suleimanov V. I. Bregadze N. A. Koval’chuk N. N. Godovikov and I. P. Beletskaya Dokl. Akad. Nauk SSSR 1983 270 343.