3 Boron By M.A. BECKETT Department of Chemistry University of Wales Bangor LL57 2U W UK 1 Introduction This report takes a similar format to that used last year’ and reviews the chemistry of boron-containing compounds reported during 1994. The literature has been surveyed by use of Chemical Abstracts volumes 120 and 121 in conjunction with independent searches of BIDS and the principal chemical journals. 2 Reviews and Articles of General Interest The reader is directed specifically to two chapters in the Specialist Periodical Report ‘Organometallic Chemistry’ (Volume 24) for two reviews complementary to this report. The first review is a comprehensive account of the chemistry of carbooranes and metallocarboranes,2“ and the second review is a general account of the organometallic chemistry of Group 13 elements.2b The Eighth International Meeting on Boron Chemistry IMEBORON VIII took place in Knoxville Tennessee USA on July 11-15 1993.Lectures have now been published in The Royal Society of Chemistry publication ‘Current Topics in the Chemistry of Boron’ dedicated to the conference proceedings.’“ In total the seventy- one articles contained in this book have been categorized into one of six topic areas organoborane chemistry chiral organoboranes medical applications of boron carborane chemistry heteroborane derivatives and complex borohydrides and metalloborane chemistry. A high quality is maintained from all contributors and the book as a whole makes stimulating reading. Plenary lectures from the conference were also published in ‘Pure and Applied Papers of general interest this year include ‘The topology of coordination polyhedra M.A. Beckett Annu. Rep. Progr. Chem. Sect. A Inorg. Chem. 1993 90,Chapter 2 3. (a)C. E. Housecroft in ‘Organometallic Chemistry’ ed. E. W. Abel Specialist Periodical Report The Royal Society of Chemistry Cambridge Vol. 24 Chapter 3 p 26; (h) K. C. Molloy in ‘Organometallic Chemistry’ ed. E. W. Abel Specialist Periodical The Royal Society of Chemistry Cambridge Vol. 24 Chapter 4 p 48; (c) ‘Current Topics in the Chemistry of Boron’ ed. G. W. Kabalka The Royal Society of Chemistry 1994 Cambridge UK; (d) M.F. Hawthorne X. Yang and Z. Zheng Pure Appl. Chem. 1994 66 245; (e) P. Paetzold J. Miiller F. Meyer H.-P. Hansen and L. Schneider ibid.255; v) S. G. Shore ibid. 263; (g) R. B. King Polyhedron 1994,13,2005;(h)Y. V. Roberts and B. F. G. Johnson J. Chem. SOC.,Dalton Trans. 1994 759; (i) A. Derecskei-Kovacs B. I. Dunlap W. N. Lipscomb A. Lowrey D. S. Marynick and L. Massa Inorg. Chem. 1994,33 5617; (j)W. N. Lipscomb and L. Massa ibid. 5155; (k) M. D. Fryzuk B. R. Lloyd G. K. B. Clentsmith and S.J. Rettig .I. Am. Chem. SOC. 1994 116 3804; (I) R. Quyoum Q. Wang M.-J. Tudoret and M. C. Baird ibid. 6435; (m)D. C. Bradley Polyhedron 1994,13,1111;(n) D. E. Kaufmann and A. Otten Angew. Chem. Int. Ed. Engl. 1994 33 1832. 19 M. A. Beckett and their rearrangements’,2g ‘Dicarbadodecaborane rearrangements an appraisal of rotational mechanisms’,2h ‘Quantum chemical studies of boron fullerene analogues’,2’ and ‘Conjunct0 closo boranes and relationships to dual structures’.2j Unusual coordination behaviour of LiCBEt,] and NaCBEt,] is shown in binuclear palladium complexes with bridging hydrides,2k and [MeB(C6F,),] -has been shown to act as a carbocationic olefin polymerization initiator in [(q5-C,Me,)TiMe2][MeB(C,F,),].2’ A review concerned with metallo-organic precursors for depositing inorganic electronic materials has been published; it contains a section on the deposition of borides.,” The use of selective anion receptors from neutral boron-containing materials has been highlighted and reviewed.,” 3 Polyhedral Species Boranes.-Pulsed laser ablated B atoms reacted with H upon condensation with excess argon to yield BH a (H,)BH complex and B,H as the major products; product molecules have been identified from TR spectra by loB and D substitution and MBPT(2) calculations of vibrational frequencies.,“ Boron- 11NMR evidence has been reported for the stepwise generation of [BH3I2- and [B,H,I2- as discrete stable intermediates in the reduction of B2H6 by alkali metal naphthalides in thf; [B,H,] -and [BHJ were formed as the final product^.^' The molecular structures of 2,4-ethanotetraborane(lO) B,H,(CH,), and 1-(difluorobory1)-pentaborane(9) 1-(F,B)B,H, have been determined in the gas-phase by electron diffraction method^.^^^^ The structural parameters of these molecules agreed well with ab initio (MP2/6-31G*) optimized molecular geometries and the experimental NMR data agreed with IGLO calculated chemical shifts.The synthesis of [B,H,,-PMe,]- from B,H,.PMe and KH or NaCHBBu;] and its reactions with BCl or HCl to yield B,H,.PMe or B,H,,*PMe, respectively have been reported; the B,H,,-PMe adduct is described as the 1-isomer rather than the 2-isomer which is believed to be the product upon addition of a Lewis base to B,H ,.3e Three of the six possible linkage isomers of SnPh,(B,H,) have been reported from the reaction of K[B,H,] with SnCI,Ph,.3f The reported isomers were p-p’-SnPh,(B,H,), p-2’-SnPh,(B5H8), and p-1’-SnPh,(B,H,),(Figure 1) and a single crystal X-ray structural determination of the latter has been ~ndertaken.~f The gas-phase molecular structures of B,H, and B,H, have been redetermined by a combination of electron diffraction and ab initio computational techniques.The new geometries have improved R factors over the previously reported structures and calculated “B NMR chemical shifts (DZ/GED level) based on the new geometries (a)T.J. Tague Jr. and L. Andrews J. Am. Chem. Soc. 1994,116,4970;(h) R. A. Godfroid T. G. Hill T. P. Onak and S.G. Shore ibid. 12 107; (c) D. Hnyk P.T. Brain D.W.H. Rankin H.E. Robertson R. Greatrex,N. N. Greenwood M. Kirk M. Buhl and P. von Rague Schleyer Inory. Chem. 1994,33,2572:(d) P. T. Brain D. W. H. Rankin H. E. Robertson 1. L. Alberts M. Hofmann and P. von Rague Schleyer ihid. 2565; (e)P. Grundt and G. Kodama ihid. 2056; v) H. Fang D. Zhao L. Brammer and L. Barton J. Chem. Soc. Chem. Commun. 1994 1531; (g) P.T. Brain D. Hnyk D. W.H. Rankin M.Biihl and P. von Rague Schleyer Polyhedron 1994 13 1453; (h)T. P. Onak and R. E. Williams Inorg. Chem. 1994 33 5471; (i) A.M. Mebel K. Morokuma and D.G. Musaev J. Am. Chem. Soc. 1994 116 3932; (j) D. Dou I. J. Mavunkal J. A. K. Bauer C. B. Knobler M. F. Hawthorne,and S.G.Shore Znorg. Chem. 1994,33,6432;(k) S. A. Jasper Jr. R. B. Jones J. Mattern J. C. Huffman and L. J. Todd hid. 5620; (1) F. Meyer P. Paetzold and U. Englert Chem. Ber. 1994,127,93;(m)D. F. Gaines A. N. Bridges and R. K. Hayashi Inorg. Chrm. 1994,33 1243; (n)F. Meyer U. Englert and P. Paetzold Chem. Ber. 1994 127 853; (0) T. Jelinek J.D. Kennedy B. Stibr and M. Thornton-Pett J. Chem. Soc. Chem. Commun. 1994 1999. Boron 21 Figure 1 Reaction of Ph,SnCl,with [BsHs] -(Reproduced from J.Chem. Soc. Chem. Commun. 1994 1531) were in good agreement with experimental data.3s The structures of nido-y-2,3-(Me2B)B,H and nido-2-MeB6H,(y-3,4-H) with unsymmetrical bridge hydrogens have been reconfirmed via the ab initio/IGLO/NMR method.3h Cluster rearrangements in the pentagonal pyramidal clusters B6H, and [(h-B,H,)(CO)(PH,),] have been studied by computational methods at the MP2/6- 31G" and HF/6-31G levels.,' The reaction of [Et,NH],[B,oH,,J with MeCN in the presence of CF,COOH yielded [Et3NH][2-B,,H,NCCH,].3j This was in contrast to an earlier report that the 1-isomer was produced in a similar reaction in the presence of p-toluenesulfonic acid. The NMR spectra and X-ray structure of [NEt,H]-[B ,H,NCCH,] was reported. The reaction of[L,PdCl,] (L = PMe,Ph SMe,) with Li2[Bl,H,,~ or Li,[B,,H,,] at room temperature resulted in L di-substituted neutral boranes characterized by NMR spectroscopy 1,10- (PMe Ph) B ,H 1,6- (PMe P h),B ,,H 8 1,7-(PMe,Ph),Bi 2H 10 1,12-(Me,S),Bl 2H 10 1,7-(Me,S)2B 2H10 and 2,7(8)-(PMe,Ph),B,,H,.3k The latter compound which exists as a mixture of enantiomers has been characterized by X-ray crystallography.B,,H,,(SMe,) reacted with the phosphaalkyne PCBu' to form a product [BloH,,(SMe,)][CButPH][B,oH,2] in which the two {B,,) units are linked by a HP-CBu' bridge (Figure 2).3' The reaction of Na[B,,H,,] with CIBH,-SMe and proton sponge or the reaction of B,,H, with ClBH,.SMe and 2NaH led to nido-[B ,HI,] -.,"' Application of these reactions using 6-alkyldecaboranes (e.y.6-thexyldecaborane) provided the first synthesis of 7-substituted monoalkyl-undecaborane anions via regiospecific boron insertion chemistry. Condensation of two molecules of B,H,,(NHEt) at 140"C yielded the conjunct0 M. A. Beckett 0 BH B A + ,u-H Figure 2 Reaction ofB,,H,,(SMe,) with PC'Bu (Reproduced by permission from Chem Ber. 1994 127 93) boraneB,,H,,(l\iHEt,) whichcould be deprotonated to theanion [B,,H,,(NHEt,)]- which has been characterized by X-ray diffraction as its [NEt3(CH2Ph)]+ salt.," The compound Unti-BI8H2 has been shown to react with MeNC in an unusual reaction which led to 7-{ (MeNH)C,N,HMe,}-anti-B 8H20 with an imidazole-based carbene coordinated to the macropolyhedral cluster (Figure 3).,O Metal1oboranes.-Progress was made on metal-rich metalloboranes during 1994.4a-g The mixed-metal metallaborane B,H,FeCo(CO) was obtained in good yield from the reaction of [co,(C0)8] with B,H,Fe,(C0),.4a Deprotonation of [y-HFe,(CO),(p- CO)(p,-HB-)I with LiBu" yielded the dianionic species [Fe,(CO),(p3-HBC0)I2 -which has been characterized by spectroscopy; reaction of this anion with protons led to decomposition whilst reaction with FeCl led to [Fe,(CO),(p-CO)(p,-HBCl)] -which has been characterized by X-ray diffraction as its [AsPh,]' A facile reaction of [Fe,(CO) ,HBI2 -with either [Fe,(CO),] or [Fe(CO),(cis-cyclooctene)] led to sequential formation of [HFe,(CO),,B]2- [HFe,(CO),7B]2- and [HFe7(CO),,B]2-;the latter anion has been characterized crystallographically as its [AsPh,] salt which showed the boron atom residing inside a monocapped trigonal + prism of Fe atoms.4c The relationship between the geometric and electronic structures for metallaboranes with {M4B4) cluster cores has been explored by approximate (Fenske-Hall) molecular orbital theory.4d The butterfly cluster [Ru,H(CO),,BH(y- NCHMe)] which contains a semi-interstitial boron atom was prepared by photolysis of [Ru,(CO),BH,] in acetonitrile in the presence of [M(CO),] (M = Cr Mo W).4e The boride cluster anions [Rh,Ru,(CO),,B] -and [Rh,Ru,(CO),,B,]- have been characterized as being octahedral and double-prismatic by X-ray diffraction studies on the [N(PPh,),] salts; these compounds were formed together with the neutral + (a) C.S. Jun T. P. Fehlner Oryanometallics 1994 13 2145; (6) L.E.Crascall B. H. S. Thimmappa A. L. Rheingold R. Ostrander and T. P. Fehlner ibid. 2153; (c) A. Bandyopadhyay M. Shang C. S. Jun and T. P. Fehlner Znoi-g.Chem. 1994,33,3677; (d)T. P. Fehlner J. Organornet. Chem. 1994,478,49; (e)J. R. Galsworthy C. E. Housecroft J.S. Humphrey X. Song A. J. Edwards and A. L. Rheingold J. Chem. SOC. Dalton Trans. 1994 3273; v) J. R. Galsworthy C. E. Housecroft and A. L. Rheingold ibid. 2359; (y) J. R. Galsworthy C. E. Housecroft D. M. Matthews R. Ostrander and A. L. Rheingold ibid. 69. Boron 23 Figure 3 Molecular structure of [7-(MeNH)C2N2HMe,]-anti-B,,H, (Reproduced from J. Chem. Soc. Chem. Commun.,1994 1999) [Rh,Ru,H(CO) 6B] by treating [N(PPh,),][Ru,(CO),BH,] with [{Rh(CO) Cl}2] .4f The reaction of [N(PPh,),] [Ru,(CO),(B,H 5)] with [{ MCp*Cl,) ,] (M = Rh Ir) followed different routes depending upon M;for Rh one of the products is the 62-electron butterfly borido-cluster [RhRu3Cp*H(CO),BH2] whilst the Ir reactant led to the 64-electron cluster [I~RU~C~*H(CO),,BH,].~~ A number of papers appeared during 1994 concerning tetrahydroborates and their coordination cherni~try.~"-~ The osmium complex [OsHCl(CO)(PPr',),] was found to react with Na[BH,] and initially gave the tetrahydridoborate complex [OsH(y2-H,BH,)(CO)(PPr',),] which was isolated and characterized; in the presence of isopropanol it decomposed to the tetrahydride [OsH,(CO)(PPr',),] .5a The structure and reactivity of [Al(BH,),] has been studied by ab initio calculations taking into account correlation energy; changing the coordination mode from (y2 +y3) of one of the borohydride groups led to the y2,q2,q3 structure which is believed to be the transition state of the hydrogen exchange mechanism observed in 'H NMR spectros~opy.~~ [Al(BH,),] reacted with CO at ambient temperature to give BH,-CO (a)M.A. Esteruelas Y. Jean A. Lledos L. A. 010 N. Ruiz and F. Vol.atron Inorg. Chem. 1994,33,3609; (b)I. Demachy and F. Volatron ibid. 3965; (c)A. J. Downs and L. A. Jones Polyhedron 1994,13,2401;(d) K.S. Siddiqi F.M.A. M. Aqra S.A. Shah and S.A.A. Zaida ibid. 247; (e) D. Coucouvanis A. Hadjikyriacou,R. Lester and M. G. Kanatzidis Inorg. Chem. 1994,33 3645; (f) T. Arliguie M. Lance M. Nierlich J. Vigner and M. Ephritikhine J.Chem. Soc. Chem. Commun. 1994 847. M. A. Beckett and a colourless viscous liquid identified as [A1H(BH,),],.5c The interaction of GeCl and SnC1 with excess K[BH,] in dry thf led to the formation of [M(BH4),] (M = Ge Sn) in which the [BH,]- anion is coordinated to the Group 14 metal atom in a tridentate manner. 5d New zirconium thiolate complexes have been obtained from the acidification of [Zr(BH,),] with RSH; [Zr,S,(Bu'S),(BH,),(thf),l and [zr6s6(BU's),(BH,)8(thf)2] were obtained from Bu'SH.'' The anion [(BH,),U(p,q7,q7-C7H7)U(BH,),] -has been obtained by treatment of [U(BH,),] with K[C,H,] and the cation [U(BH,),(thf),]+ was produced by protonation of [U(B H ,),(t h f ),]with [NH E t ,][BPh,] in t h f. There have been fewer publications on boron-rich metalloboranes during 1994 than in previous years.6aA The reactions of [(Cp*CoCl},] with BH,.thf and Li[BH,] have been described; products include nido-1-{C~*CO)-~-((~~-C,M~,H)CO)B,H, arachno-Cp*CoB,H o nido-(2,4-Cp*Co) *B3H7 cIoso-2,3,4-(Cp*Co) 3B2H4 and closo-l,2,3-{Cp*C0},B,H,.~~ The analogous chromium dimer [{Cp*CrCl},] was found to react with BH,.thf to result in a brown diamagnetic solid [{Cp*Cr),B,H,] whose structure is believed to be similar to that of [(cp*Ta),(B,H,),] but with a Cr-Cr triple bond.6h The capped-closo species [1-(FeCp)-2-{Mo( PMe Ph),H)B ,H 7] has been prepared from the reaction of nido-[2-(FeCp)B5H with [Mo(PMe,Ph),H,] and has been characterized crystallographically (Figure 4) and by NMR spectroscopy; the structure reveals one Fe-Mo-B face capped by a boron atom and the other capped by a triply-bridging hydrogen atom.The isostructural W compound [1-{ FeCp}-2-{W(PMe,),H) B ,H 7] and nido-[2-(Re( PMe,),B,H 0] were reported.6' The metallaborane anions [Cu(Bl ,H and [Ni(B,,H 1)2]4-have been prepared from the reaction of [Me,NH][B ,HI,] in aqueous NaOH with CuO or NiCI, respectively. NMR XPS and cyclic voltammetry results were reported together with a single crystal X-ray diffraction study on [NBu;] CCu(B1,H 11121.6d Heteroboranes-The reader is directed to a Royal Society of Chemistry publication 'Specialist Periodical Report Organometallic Chemistry' for a comprehensive review of the 1994 literature concerning carbaboranes.'" The reaction of Me,Si(C-CMe) with excess Et,BH has been shown to sponta- neously lead to the formation of the endo-and exo-isomers (55% and 45% respectively) of the arachno-1-carbapentaborane(10) derivative [{p-2,5-C(Et)(SiMe,H)]-1-CEt-2,3,4,5-(BEt),H3]; this cluster type appears to be very stable and must be taken into consideration upon future investigations of multiply C-borylated organic cornpo~nds.~" A derivative with an ortho-phenylene link (a)Y.Nishihara K. J. Deck M. Shang T. P. Fehlner B. S. Haggerty and A. L. Rheingold Organometallics 1994,13,4510;(b)K. J. Deck Y. Nishihara M. Shang and T. P. Fehlner,J. Am. Chem. Soc. 1994,116,8408; (c)H. J. Bullick P. D. Grebenik M. L. H. Green A. K. Hughes J. B. Leach and P. Mountford J. Chem. Soc. Dalton Trans. 1994 3337; (d) J. G.Kester D. Keller J.C. Huffman M. A. Benefiel W. E. Geiger Jr. C. Atwood A. R. Siedle G.A. Korba and L. J. Todd Inorg. Chem. 1994 33 5438. ' (a)R. Koster G. Siedel and B. Wrackmeyer Angew. Chem. Int. Ed. Engl. 1994,33,2294;(b)B. Gangnus H. Stock W. Siebert M. Hofmann and P. von Rag& Schleyer ibid, 2296; (c)M.A. Fox R.Greatrex M. Hofmann P. von Rague Schleyer ibid. 2298; (d) J. PleSek B. Stibr X. L. R. Fontaine T. Jelinek M. Thornton-Pett S. Heimanek and J.D. Kennedy Inorg. Chem.. 1994 33 2994; (e) M.A. Fox and R. Greatrex J. Chem. Soc. Dalton Trans. 1994,3197;v) A. Ceulemans G. Goijens and M. T. Nguyen J. Am. Chem. SOC.,1994,116,9395; (g) T. Jelinek J. Holub B. Stibr X. L. R. Fontaine and J. D. Kennedy Collect. Czech. Chem. Cornmun. 1994 59 1584; (h) J. Holub B.Stibr Z. JanouSek J. D. Kennedy and M. Thornton-Pett Inorg. Chim. Acta 1994 221 5; (i) R.H. Pak R.R. Kane C. B. Knobler and M. F. Boron 25 Figure 4 Molecular structure of the capped closo species [(FeCp){Mo(PMe,Ph),H)B,H,I (Reproduced by permission from J. Chern. SOC.,Dalton Trans. 1994 3337) 1-alkyl-(2,5-ortho-phenylene)-1-carbapentaborane( lo) has also been prepared.7b The reactions of arachno-B,H, with alkynes (MeCCH EtCCH and MeCCMe) to yield alkyl derivatives of arachno-pentaborane( 10) have been described; reported and characterized compounds include l-R-1-C-(p-2,5-X)B4H (R = Me X = CH, endo-CHMe exo-CHMe; R = H X = endo-CHMe exo-CHEt; R = Et X = CH,) with structures supported by IGLO chemical shift calc~lations.~~ The monocarbaborane base adducts endo-9-Me-8-(NMe3)-arachno-6-CB,H , 9-Me-8-L-nido-6-CB9H (L = NMe, OH-) and exo-6-L-arachno-4-CB8H12(L = SMe, NMe, urotropine pyridine quinoline MeCN PPh, and MeNC) have been prepared from the regiospecific cluster degradation reactions of closo-1,2-C,BloH ,in the presence of Lewis base (L) which proceeded via the nido-[7,9-C,BloHl,] -anion intermediate.7d The true identity of the 'bare-carbon' cluster 'closo-C,B,H,' has been revealed as closo-2,3-C2B,H by careful re-evaluation of reported NMR data.,' A detailed ab initio study of the rearrangement of C,B,H revealed that the carborane is fluxional along the closo-nido opening mode and could rearrange via a consecutive double diamond-square-diamond me~hanism.,~ Deprotonation of the neutral arachno-C,B,H, with either proton sponge or K,C0,/[NMe4]C1 led to the formation of the arachno anion [4,5-C,B7H ,] -in high yield; new nine-vertex hypho-dicarbaboranes (R exo-5-(NR,)-hypho-4,9-C2B7H13= Me Et) have been prepared by the addition of NR to C2B,H ,in CH,Cl solution whilst reaction with NaCN in aqueous solution resulted in removal of one boron vertex and the generation albeit in small yield of the eight-vertex hypho-[7,8-C,B,Hl,] -anion.7g NH,Pr" and NH when reacted with nido-5,6-C,B,Hl in CH,Cl at room temperature gave the exo-9-L-arachno-5,6- Hawthorne Inory.Chern. 1994 33 5355; (j)D. Hnyk P.T. Brain H. E. Robertson D.W. Rankin M. Hofmann P. von Rague Schleyer. and M. Buhl J. Chern. SOC.,Dalton Truns. 1994 2885 (k) D. Hnyk D.W. H. Rankin H. E. Robertson M. Hofmann P. von Rague Schleyer and M. Biihl Inorg. Chern. 1994 33 4781. M. A. Beckett C,B,H, ligand derivatives whereas the tertiary amines (L = NEt, NBu:) afforded isomeric compounds exo-6-L-5,10-C,B8H 2; the parent anion arachno-[5,10-C2B8H,,] -has been prepared from the reaction of exo-6-(NEt,)-5,10-C2B,H, with Na metal in thf.7h The synthesis and structural characterization of [Me,NH][nido- 9,l 1-12-7,8-C,B,Hlo] and [Me,NH][nido-9-I-7,8-C2B9H1 ,] have been rep~rted.~' The molecular structures of 1 ,7-C12- 1,7-dicarba-closo-dodecaborane( 12) (1 ,7-C12-1 ,7- C2B,,H,,) and 1,2-dicarbadecaborane(lO)(C2B8H10) have been studied by electron diffraction methods and icosahedral and bicapped square antiprimatic structures modelled; the reliability of the experimental structures was assessed by ab initio (MP2/6-31" level) optimized structures in concert with IGLO calculations on "B NMR chemical ~hifts.~j*'~ There has been considerable progress in aza-,"" and thiaboranesdPh chemistry during 1994.Thus reactions between arachno-4-NB8H ,with Lewis bases (py quin isoquin urotropin and MeCN) have lead to the isolation and characterization of exo-6-L-arachno-4-NB8Hl adducts." A new route to closo-NB ,H, has been described starting from nido-NB,H, by interaction with Me,S-BH at 140 "C to form closo-Me,SBH,NB ,H ,;the N-bonded ligand to Me,SBH was removed with Bu'NH~.'~ The first macropolyhedral eighteen-vertex azaborane anti-9-NB1 7H, has been obtained from n-butylnitrite and anti-B,,H, in 1&15'/0 yield; it was character- ized by NMR and MS measurements.8' The first nido-thianonaborane nido-[9-S- B,H,] -has been prepared from deprotonation of exo-6-(SMe2)-arachno-4-sB8Hlo by NaH or Na metal; it could be reconverted back into the exo-L-arachno-4-SB8H, series (L = SMe, py) by action of the Lewis base followed by acidification with CF3COOH.8dA series of these eXo-L-UrUChno-4-SB8Hlo clusters (L = SMe, PPh, MeCN NMe, py urotropine MeNC quin) have been prepared from arachno-4- SB8H12 or nido-6-SB,H1 ,and the corresponding Lewis bases; X-ray crystal structure of three representative adducts (L = urotropine 1/2urotropine MeNC) have been reported.8e The reaction of [nido-6-SB,H1 ,I-with s8 resulted in the 11-vertex arachno-dithiaborane cluster anion [2,3-S2B,H,,] -.sf Reactions of [arachno-2,3-S,B,H,,]-with H2S0, MeI and CH,12 have been reported and dehydrogenation of arachno-2-H-2,3-S,B,Hlo gave the previously described compound nido-7,9-S2B,H,.8f Thermolysis of arachno-4-SB,H1 in cyclohexane has been shown to generate the eighteen-vertex macropolyhedral anti-9,9'-S,B,,Hl in modest (1 8%) yield.8g The macropolyhedral anion [S,B,,H,,]- isolated in 48% yield as its [PPh,] + salt has been obtained from the action of elemental sulfur on a solution of the anti-[B ,H2,I2- anion and has been characterized by X-ray diffraction (Figure 5)and (a) T. Jelinek B. Stibr and J. D. Kennedy Collect. Czech. Chem. Commun. 1994,59,2244;(b)L. Schneider U. Englert and P. Paetzold Chem.Ber. 1994,127,87; (c) T. Jelinek J. D. Kennedy and B. Stibr J. Chem. Soc. Chem. Commun. 1994 677; (d)J. Holub J. D. Kennedy and B. Sibr Collect. Czech. Chem. Commun. 1994,59,367;(e)J. Holub B. Stibr,J. D. Kennedy M. Thornton-Pett,T. Jelinek and J. PleSek Inorg. Chem. 1994,33,4545; (f) J. Holub A. E. Wille B. Stibr P. J. Carroll and L. G. Sneddon Inory. Chem. 1994,33 4920; (y) T. Jelinek J. D. Kennedy and B. Stibr J. Chem. SOC.,Chem. Commun. 1994,1415; (h)T. Jelinek J.D. Kennedy B. Stibr and M. Thornton-Pett Angew. Chem. Int. Ed. Engl. 1994 33 1599; (if N.S. Hosrnane K.-J. Lu A. K. Saxena H. Zhang J. A. Maguire A. H. Cowley and R.D. Schluter Orgunometal-lics 1994 13 979; (j)N.S. Hosrnane L. Jia H. Zhang and J. A. Maguire ibid. 1411; (k) J. Holub J. D. Kennedy T.Jelinek and B. Stibr J. Chem. Soc. Dalton Trans. 1994,1317; (I) M. L. McKee Inorg. Chem. 1994 33 6213; (m) E. D. Jernrnis G. Subrarnanian and G. N.Srinivas ihid. 2317; (n) E. D. Jemrnis G. Subramanian and B. V. Prasad ibid. 2046. Boron 27 U Figure 5 Molecular structure oj the macropolyhedral [S,B,,H Janion (Reproduced by permission from Angew Chem. Znt. Ed. Engl. 1994 33 1600) NMR spectroscopy; the principal other product from this reaction was the known nido-[7-SBl,Hl 1]-anion (45%).8h The synthesis of c2oso-indacarbaboranes and their reactions with the bis(bidendate) Lewis base 2,2’-pyrimidine have been studied; the crystal structures of closo-l- (Me,CH)-1-Tn-2,3-(SiMe,),-2,3-C,B4H4 and 1 -(2,2’-C8H6N,)-1 -(Me,CH)-1 -In-2,3- (SiMe,),-2,3-C2B,H have been described.8i The synthesis reactivity and spectro- scopic properties of the ‘carbons-apart’ closo-l-Sn-2-(%Me,)-4-(R)-2,4-C2B4H4 and the crystal structures of the donor-acceptor complexes l-Sn(L)-2,4-(SiMe3),-2,4-C,B,H (R = SiMe, Me; L = 2,2’-CloH8N, 2,2’-C8HnN4 and [CpFe(yS-C,H,CH,NMe,)]) have been reported.8j The new ten-vertex carbathioaborane arachno-6,9-CSB8H, has been prepared by the reaction of arachno-4-CB8H14 with elemental sulfur and triethylamine in chloroform solution.8k A series of further thiacarbaborane species have been prepared from this compound arachno-[6,9-CSB8Hl1] - nido-7’9-CSB,Hl 1 arachno-4,6-CSB,Hl 1 nido-[6,9-CSB8H,] - and hypho-[7,8-CSB6Hl 1] -.8k A series of 9-and 10-vertex nido and arachno heteroboranes have been studied by ab initio methods (HF/6-31G*) and bond distances found to be in good agreement with X-ray data.8z ab initio MO studies on a series of pyramidal B,H,X structures (X =NH+ N CH EH- P PH’ SiH NO PO Co(CO),} indicate that for X = NH+ N and NO the terminal hydrogens of the basal ring pointed towards the direction of the capping group whilst with the other capping fragments these hydrogen atoms pointed away from the cap.8m A theoretical study on the isomer preferences of the 5- 6- and 7-vertex monoheteroboranes has been published.8” Metal1oheteroboranes.-A dimeric metallaheteroborane [(Pd(PPh,)(S,B,H,)},] with heteroatoms acting as both cluster atoms and two-electron donor sites has been obtained from the attempted recrystallization in MePh/CH,CI of a product obtained from the reaction of [PdCl,(PPh,),] with hypho-[7,8-S,B6H,] -;the dimeric product M.A. Beckett has been characterized cry~tallographically.~" Reactions of [MCI(PPh,),] (M = Rh Ir) with arachno-[S,B,H,,] -yielded cluster species nido-[(PPh3),HIrS,B,H9] nido-[(PPh,),HRhS,B,H,] nido-[(PPh,),RhSB,H,,1 and a complex [(PPh,),H,Ir(S,B,H,,)] in which the cluster-metal interaction occurred solely via a heteroatom q1 two-electron/two-centre cluster-to-metal donor bond.9b Ten vertex polyhedral azametallaborane chemistry has been developed with the preparation of arachno 9-((PMe2Ph),Pt}-6-NH-B8Hlo and nido 8-{ArRu)-6-NH-B,HlO (Ar = C&, MeC,H,Pr') species from reactions of cis-[PtCl,(PMe,Ph),] or [(Ar- RuCl,),] with appropriate azaborane The rhodium atom in the rhodatelluradodecaborane( 12) c/oso-2-(Rh(PPh,)(PhNHCS2))-1-Te-B ,H , is bonded to a triphenylphosphine and a N-phenyldithiocarbamate ligand; the Rh-Te distance is 2.5812(3)A and the structure is consistent with Wade's rules with the { Rh(q2-S,CNHPh)(PPh3)) unit equivalent to (BH} and the 'naked' {Te) cluster vertex equivalent to {BH2-).9d A c ombination of arachno-4'6-CSB7H cis-[PtCl,(PMe,Ph),] and a base (proton sponge) have been reacted to furnish the arachno cluster 9-{Pt(PMe,Ph),}-6,8-CSB7H9 in 41 % yield; thermolysis of this com- pound resulted in ortho-cycloboronation rather than cluster degradation to afford 9.9-(PMe,Ph)(PMe,-ortho-C6H~)-~ruchno-9,6,8-PtCSB7H~-lO in 51% yield." Following on from last year a brief survey of the more important developments in metallocarborane chemistry is included in this section; a comprehensive review of this area is available.," Thermolysis of the metallamonocarbaborane cluster 7-((CO)(PPh3),Ir)-1 -CB,H at 250 "C resulted in isomerization to afford 7-( (CO)H(PPh,)Ir}-9-PPh3-1-CB7H7 and 7-{(CO)H(PPh,)Ir)-6-PPh3-1-CB7H7 as the major products."' These clusters have quadrilateral open faces (B-B 220 pm) and isonido geometries although of formal closo constitution (Figure 6).The reaction of [NMe4][7-SMe-8-Me-nido-7,8-(a)M. Murphy T. R. Spalding J. D. Kennedy M.Thornton-Pett K. M. A. Malik M. B. Hursthouse and J. Holub J. Chem.Soc. Chem. Commun. 1994,2403; (b)R. Macias J. Holub J. D. Kennedy B. Stibr and M.Thornton-Pett ibid.,2265; (c) J. H. Jones B. Stibr J. D.Kennedy and M. Thornton-Pett Inorg. Chim. Acta 1994,227,163; (d)G. Ferguson D. O'Connell and T. R. Spalding Acta Crystallogr. Sect. C 1994 SO 1432; (e)J. H. Jones J. D. Kennedy and B. Stibr Inorg. Chim. Acta 1994 218 1. 'O (a)B. Stibr J. D. Kennedy E. Drdakovi and M. Thornton-Pett J. Chem.Soc. Dalton Trans. 1994,229; (b) F. Teixidor C. Viiias J. Casabo A. M. Romerosa J. Rius and C. Miravitlles Organometallics 1994 13 914; (c) J. Cowie B. D. Reid J. M. S. Watmough and A. J. Welch J. Organomet. Chem. 1994,481,283; (d) K. J. Adams J. Cowie S.G. D. Henderson G. J. McCormick and A. J. Welch ibid. C9; (e)G. 0.Kyd L. J. Yellowlees and A. J. Welch J. Chem. Soc. Dalton Trans. 1994,3129; v) K. F. Shaw B.D. Reid and A.J. Welch J. Organomet. Chem. 1994,482,207; (g) G. Ferguson J. F. Gallagher M. C.Jennings S. Coughlan T. R. Spalding J. D. Kennedy and X. L. R. Fontaine J. Chem.Soc. Chem. Commun. 1994 1595; (h)Y.-W. Park J. Kim and Y. Do Inorg. Chem. 1994 33 1; (i)F. Teixidor J. A. Ayllon C. Viiias R. Kivekas R. Sillanpad and J. Casabo Organometallics 1994,13,275 1 ;0)F.Teixidor J. A. Ayllon C. Viiias R. Kivekas R. Sillanpaa and J. Casab6,'J. Organornet. Chem. 1994,483 153; (k)J. C. Jeffery P.A. Jelliss and F. G. A. Stone J. Chem. Soc. Dafton Trans. 1994 25; (I) J.C. Jeffery P.A. Jelliss and F.G.A. Stone Organomet~6~ics, 1994 13 2651 ; (m) N. Carr D. F. Mullica E. L. Sappenfield and F. G. A. Stone Inorg. Chem. 1994,33 1666; (n)K. A. Fallis D. F. Mullica E. L. Sappenfield and F.G.A. Stone ibid. 4927; (0) D. F. Mullica E. L. Sappenfield F. G. A. Stone and S.F. Woollam Organometallics 1994,13 157; (p) S. J. Dossett S. Li D. F. Mullica E. L. Sappenfield and F. G.A. Stone ibid. 822; (4)J. M. Forward D. M. P. Mingos and A. V. Powell J. Organomet. Chem. 1994 465 251; (r) Y.-K. Yan D. M. P. Mingos T. E. Muller D. J. Williams and M. Kurmoo J. Chem. Soc. Dalton Trans. 1994,1735; (s)I. Cisaiova K. Maly and L. Hummel Acta Crystallogr. Sect. C 1994 SO 198; (t) 0.Ki-ii A. L. Rheingold M. Shang and T. P. Fehlner Inorg. Chem. 1994 33 3777; (u) E. Bembenek 0.Crespo M.C. Gimeno P.G. Jones and A. Lugano Chem. Ber. 1994,127,835; (u) 0.Crespo M. C. Gimeno P. G. Jones and A. Laguna Inorg. Chem. 1994,33,6128; (w)S. Li D. F. Mullica E. L. Sappenfield and F.G. A. Stone J. Organomet. Chem. 1994 467 95. Boron 29 C(221) 7 Figure 6 Molecular structure of [(CO)(PPh,),IrCB,H,] (Reproduced from J. Chem. Soc. Dalton Trans. 1994 231) C,B,H,,] with [RuCl,(PPh,),] led to the formation of [(PPh3),Ru-7-SMe-8-Me-7,8-(5)-C2B8HllJ with a new C2B carborane ligand which has a peculiar arachno structure resulting from the elimination of B(5) from the former [C2B,Hl2]- nido precursor; the geometry is basket-like with a B-B handle.'Ob A series of papers assessing steric effects of C-substituted metalladicarbaboranes have been published."'-' Crystallographic studies on l-Ph-3-mes-3,1,2-clos-RuC,B,H, and 1-Ph-2-Me-3-(cym)-3,1,2-closo-RuC,B, 1-1 revealed that whereas the former contains an essentially undistorted (RuC,B,) framework there was some indication that in the latter a polyhedral deformation from closo towards pseudo closo had just begun."' In ((PPh,)Cu},Ph,C,B,H and {(o-tol),PCu},Ph,C,B,H one copper atom is exo-facially bonded to the B(8)B(9)B(12) triangular face whilst the other copper atom occupies a polyhedral vertex position but is slipped away from the cage carbons; this slippage was more marked in the (0-tol),P derivative."" The compounds 1-Ph-3-(cod)-3,1,2-MC,B,H,,(M = Pd Pt) 1,2-Ph2-3-(cod)-3,1,2- PdC,B,H, and 1,11-Ph2-3-(cod)-3,1,1 1-PtC2B9H have been prepared from reac- tions between Tl,[7-Ph-nido-7,8-C,B9Hlo] and or T1,[7,8-Ph,-nido-7,8-C2B9H9] [MCl (cod)].The structure of (cod)PdPh,C,B,H revealed severe intramolecular crowding with the Pd atom slipped by 0.56 8 away from the phenyl groups and the cage deformed with extended C-B distances in the ligand face.'" Eight new complexes of mono- and di-ether carboranes with Ru Rh Pd Pt Hg La and U as metal vertices have been prepared by reactions between appropriate metal substrates and either a suspension of Tl,[7-CH,OMe)-7,8-nido-C2B9Hlo] or M2[7,8-(CH2OMe),-7,8-nido-C,B,H,] (M = T1 Li); crystallographic studies revealed that as the formal coordina- tion number of the metal decreased there was an increased interaction between the pendant ether oxygen atom@) and the metal atom.lof Novel phosphonium-betaine ligands [SC(H)PPh,] -and [S(H)C=C(PPh,)S] -have been stabilized in the 12-vertex closo rhodacarborane complexes [3-(q2- M.A. Beckett n Figure 7 Molecular structure of [(Ag(SbPh,)}2(C2B,H,2)2] (Reproduced by permission from Inorg. Chem. 1994,33 2) SC(H)PPh,)-3-(PPh,)-3,1,2-RhC2B,H,and [2-{q2-S(H)C=C(PPh,)S}-2,1 ,7-J RhC2B,Hl which were characterized by X-ray diffraction and spectroscopic methods.log A brief account of the synthesis and structure of the dimeric argentacar- boranes [9,9'-{Ag(EPh,)2}2-4,9,4,9'-(p-H,)-7,8,7',8'-nido-(C2B9Hlo)2](E = As Sb) has appeared; the molecular structure of the SbPh derivative is shown in Figure 7."" Sixteen exo-ruthenium@) complexes derived from [7,8-p(SRS)-7,8-C2B9Hlo]-ligands (R = CH2 (CH2)2 (CH2)3 (CH2)4 {CH2CH20CH2},, {CH2CH20CH2CH2}20) have been prepared and characterized; the ruthenium(i1) centres are bound to the clusters via two S-donor interactions and a bridging Ru-H-B(3) bond with the length of the S,S' connecting chain modifying the Ru-B(3) distance."' The crystal structure of [(PPh3)Hg{7,8-p-(SCH2S)-7,8-C2B9H9}] has been determined and shows that the Hg" centre is coordinated to the three boron atoms in the (C2B3) 'open-face' of the ligand."j New gold carbaborane complexes have been prepared from [NEt4][ 10-endo-(Au(PPh,))-7,8-Me2-nido-7,8-C2B,H9] and [AuCI(PPh,)] ;a di-gold and a tri-gold species have been structurally characterized.lok The reactions of the new aura- carborane reagent TI[10-endo-Au(tht)-7,8-Me,-nido-7,8-C2B9H9] with the Boron 31 alkylidyne(cyclopentadieny1) metal complexes [M(CR)(CO),Cp] (M = Mo W; R = aryl) have been studied; products described include [NEt4][[ lO-endo-{ AuW(p CC,H,Me,-2,6)(CO),Cp}-7,8-Me2-nido-7,8-C2B9H9] and [9,9'-exo-(Au,Mo(p,-CC,H,Me-4)(CO),Cp}-7,7',8,8'-Me,-nid0-7,7',8,8'-(C~B~H~)~].~~~ The synthesis protonation and ligand substitution reactions of anionic allyl(carborane) complexes (derived from e.g.nido-7,8-Me,-7,8-C,B9H9) of Ni Pd and Pt have been de- scribed.lorn,' Treatment of the salts [NEt,][Mo(CO),(q3-C3Hs)(qs-7,8-R,-7,8-C2B,H,] (R = H Me) with [CPh,][BF,] in CH,CI in the presence of donor molecules (L) afforded the cluster substitution products [Mo(C0),(q3-C,H,)(qs-7,8-R,-7,8-C,B9H,-10-L)] (R = H L = OEt,; R = Me L = OEt, thf SMe, PPh, py) and the structure of [Mo( C0) ,(q -C H ) (q -7,8 -Me ,-7,8 -C ,B H -10-0E t ,)] has been established by X-ray crystallography.loo The reactivity of bis(a1kyne) carborane complexes of Mo and W (e.g. [Mo(CO)(q2-MeC,Me),(q5-7,8-Me2-7,8-C2B9H9]) towards Bu'NC has been reported.loP The salts [FeCpz][M(C,B,H,,),] (M = Cr Fe Ni) have been prepared from the metathesis of [FeCpzICl and [NMe,][M(C,B,H 1)2].'0q These three salts were isostructural with one another and magnetic studies showed that they obeyed the Curie-Weiss law between 6 and 296K. The synthesis and structure of the charge compensated ferracarborane [3,3'-Fe(4-(Me,S)-1,2-C2B9H ,,},I and its charge-trans- fer salt with 2-3-dichloro-5,6-dicyano-p-benzoquinone was reported; magnetic measurements were also discussed.lorThe crystal structure of the bridged bis(dicarbadodecaborane)cobalt(m) cluster [8,8'-p-(MeOCOCH2NH)-3,3'-Co-1,2,1'2'-(C2B9Hlo) has been published."" The synthesis of metal carboxylates [M'1(1,2-C,B,oH,,C0,),] (M = Zn Cu Ni and Mo) and [M"{1,2-C,B,,H,,(CO,),f] (M = Cu Ni) have been reported and compounds were characterized spectroscopically; the thermolysis of these species has been investigated by weight loss TR spectroscopy and the isolation of volatile products.Or Solid state products from this thermolysis were characterized by elemental analysis powder X-ray diffraction and X-ray photoelectron spectroscopy.' Or Silver and gold complexes of the bis(diphenylphosphany1)-o-carboraneligand have been AgX (X-= [ClOJ [NO,]-) reacted readily with (PPh,),C,BloHlo to form complexes [AgX(PPh,),C,B,,H,,]; when X = [ClO,] -ligand displacement reactions readily afforded three- or four-coordinate Ag' com-plexes [AgL(PPh,),C,B,,H,,][C104] (L = PPh, PMe,Ph SPPh,) [AgL,(PPh,),C,B,,H lo][CIO,] (L = phen bipy (PPh,),C,B,,H ,,).lo" A number of four-coordinate gold(1) species containing the (PPh,),C,B,,H, ligand have been reported and the crystal structure of [Au{(PPh,),C,B,,H,,)((SPPh2)2CH2}][C104]~ CH,Cl has been described.' O" The synthesis of the complexes [N(PPh,),][M(CO),(q3-C,Hs)(q6-7,9-C,BloH,,Me,] (M = Mo W) and the crystal structure of [N(PPh,),] [WBr(CO),(q6-7,9-C,BloHloMe2)] have been reported; the latter clusters are best viewed as closo 13-vertex species (Figure 8).loW 4 Metal-catalysed Hydroboration Reactions Potential energy surfaces for rhodium(1)-catalysed olefin hydroboration reactions have been studied by ab initio molecular orbital calculations at the MP2/ECP + DZ M.A. Beckett Figure 8 Molecular structure qf[WBr(CO),(C2B,,H,,Me2)] -asfound in its [N(PPh,),] + salt. (Reproduced by permission from J. Organomet. Chem. 1994 467 97) level."' Catalysed hydroborations of several 1,l-disubstituted aryl alkenes have been studied and the mechanistic implications of phosphine-to-rhodium catalyst ratios on regioselectivities and enantioselectivities have been discussed. Ib The molecular structures of B,cat and its 4-But and 33-B~ derivatives have been determined by single crystal X-ray diffraction studies; these compounds react with [((PPh,),RhCl},] and [Rh(PPh,),Cl] by oxidative-addition to yield [Rh(PPh,),(Bcat),Cl] deriva-tives.' lC Bond dissociation energies of a series of B-H and B-C bonds in boranes have been calculated and an estimate of 66kcal/mol for the Ir-B bond strength in [Ir(CO)(PPh,),ClH(Bcat)] has been obtained using the calculated B-H bond dissociation energy of HBcat (11 1 kcal/mol); this Ir-B bond dissociation energy greatly exceeds the bond dissociation energy of the Ir-Me bond in trans-[Ir(CO)(PPh,),ClMeI] of 35 kcal/mol."d The addition of HBcat to the low-valent [CpRu(PPh,),Me] complex led to the formation of [CpRu(PPh,),H] and MeBcat by a mechanism more characteristic of high-valent metal centres; kinetic data were consistent with a mechanism which proceeded via a four-centred transition state that involved partial cleavage of the B-H bond during the formation of the B-C bond."" Regioisomers of the first tantalum boryl complexes endo-[Cp,TaH,(Bcat)] and exo-[Cp,TaH,(Bcat)] have been prepared from [(Cp,TaH,Li),] in MePh at -78 "C;the single crystal X-ray diffraction structures of both regioisomers have been (a) D.G.Musaev A. M. Mebel and K. Morokuma,J. Am. Chem. Soc. 1994,116,lO 693; (b) K. Burgess and W. A. van der Donk Inorg. Chim. Acta 1994,220,93; (c)P. Nguyen G. Lesley N. J. Taylor T. B. Marder N. L. Pickett W. Clegg M. R. J. Elsegood and N.C. Norman Inory. Chem. 1994 33 4623; (d) P. R. Rablen J. F. Hartwig and S. P. Nolan J. Am. Chern. Soc. 1994 116,4121; (e)J. F. Hartwig S. Bhandari and P. R. Rablen ibid. 1839; v) D. R. Lantero D.H. Motry D. L. Ward and M. R. Smith 111 ibid.10 81 1; (9)K. Burgess and W. A. van der Donk Organornetallics 1994,13,3616; (h)H. Wadepohl G.P. Elliot H. Pritzkow. F.G.A. Stone and A. Wolf J. Organornet. Chern. 1994 482 243. Boron 33 Figure 9 ORTEP drawings of endo-and exo-[Cp,TaH,(Bcat)] (Reproduced by permission from J. Am. Chem. Soc. 1994 116 10 81 1) determined (Figure 9).'lf Although there is some evidence that the metal may be directly involved in a few cases the TiCl and [Ti(OPr'),] 'catalysed' alkene/[BH,] -hydroboration reactions have been shown to predominately involve formation of BH in situ.''g Hydroboration of the carbon-tungsten triple bonds of the Fischer-carbyne com- plexes [Cp(CO),WC(p-tolyl)] and [Cp*(CO),WC(p-tolyl)] have been demonstrated for H,B,Et where the boryl substituted q3 benzyl complexes [(C,R,)(CO),W(a-1,2- q3-BEt,((p-methyl)benzyl)l (R = H Me) were obtained; the boron-containing ligands are bound in an a,l,2-q3 enylic fashion to the tungsten atoms.'lh 5 Heterocycles Containing Boron Boron-Carbon Ring Systems.-The X-ray determined structures of the borole hydrido iron complexes [CpFeH(Me,CTB Ph)] and [(C,H4Me)FeH(2,5-Me,CXB Ph)] showed the presence of an Fe-H-B three-centre bond with a weak B-H interaction (Figure 1O).I2" A new class of amphoteric molecule having Lewis acidic and Lewis basic sties have been prepared from the reaction .of [Cp*MCl,] (M = Zr Hf) with the substituted aminoborollide Li,[C,H,B NPri].Products characterized as [Cp*M(C?B NPr',)Cl,.Li(OEt 2 ) 32-were readily protonated by HC1 to afford zwitterionic dichlorides [Cp*M -(C,H,B N+HPr',)Cl,].' 2b The 1-t-butyl-2-methyl- 1,2-azaborolyl lithium salt (LiAb) and TlCl equilibrate at -75 "C under the action of light to give LiCl and TlAb.The reaction of TlAb with Ph,PCl gave the expected Ph,P-substituted azaborole ring in high yield whilst the lithium salt reacted with Ph,PCl to give only a small quantity of this product.'2c The first sixteen valence-electron iron sandwich compound (a)G. E. Herberich T. Carstensen D. P. J. Koffer N. Klaff R. Boese I. Hyla-Kryspin R. Gleiter M. Stephan H. Meth and U. Zenneck Organometallics 1994 13 619; (b) R. W. Quan G. C. Bazan A. F. Kiely W. P. Schaefer and J. E. Bercaw J. Am. Ckem. SOC.,1994,116,4489;(c)G. Schmid J. Reschke and R.Boese Chem. Ber. 1994,127,1891; (d)W. Siebert R. Hettrich and H. Pritzkow Angew. Ckem. Int. Ed. Engl. 1994,33 203; (e) B. Gangus A. Fessenbecker H. Pritzkow and W. Siebert Ckem. Ber. 1994,127 2393; (f) C. Balzereit H.-J. Winkler W. Massa and A. Berndt Angew. Ckem.,Int. Ed. Engl. 1994,33,2306; (g) B. Deobald J. Hauss H. Pritzkow D. Steiner A. Berndt and W. Seibert J. Orgunomet. Ckem. 1994 481,205; (h)A. J. Ashe 111 W. Klein. and R. Rousseau ibid. 468 21; (i) A. Hergel H. Pritzkow and W. Siebert Angew. Chem. Int. Ed. Engl. 1994,33 1247; (j)P. Frankhauser M. Driess H. Pritzkow and W. Siebert Ckem.Ber. 1994,127,329;(k)W. Weinmann H. Pritzkow and W. Siebert,ibid. 61 1; (I) A. Kramer H. Pritzkow and W. Siebert ibid. 1047. M. A. Beckett Figure 10 Molecular structure of [(C,H4Me)FeH(2,5-Me,C,H,BPh)] (Reproduced by permission from Organometallics 1994 13 621) Figure 11 Molecular structure of [(Ni(cod)),{C,H,(BMe),C=CC4H,] (Reproduced by permission from Chem.Ber. 1994 127 2394) [Cp*Fe{B(Et)C(Me)B(Et)C(Pri)C(Pri)>] has been characterized by a single crystal structure analysis which reveals a severely folded 2,3-dihydro- 1,3-diborolyl ring. 12d The reactions of 1,4-dihydr0-1,4-diborapentafulvenederivatives with [M (co~)~] (M = Ni Pt) have yielded complexes in which the borafulvenes bridge two (M(cod)) centres as a p,q2,q5 ligand; the crystal structure of one such compound is shown in Figure 11 The first dilithium compound of a 1,3-diboratabenzene dianion Boron 35 Li,[B(Bu')CHB(Bu')C(SiMe,)C(SiMe,)C HI was cleanly prepared by reducing a nido-tetracarbahexaborane with Li in thf.' 2f The reaction was reversible and oxidation back to the tetracarbahexaborane was achieved by boiling the 1,3-diboratabenzene dianion in 1,2-dibromoethane.A related benzo-tetracarbahexaborane derivative reacted with [CpCo(C,H,),] to form a 1,3-dihydr0-1,3-diborananaphthalenecom-plex by a similar rearrangement of the ligand and displacement of ethylene.12g The barriers to rotation about B-N bonds of the 1-aminoborepins 1-(N-benzyl-N- methy1amino)borepin and l-(N-benzyl-N-methylamino)-4,5-dihydro-borepin have been determined from VT 13C NMR spectroscopy as 18 and 19.8 kcal/mol respective- ly; the corresponding rotational barriers of a variety of aminoboranes have been calculated using the semi-emperical AM 1 method.'2h The first boron bridged naphthalene has been prepared in excellent yield as a colourless crystalline solid from the reaction of Cl,BNPr' with 1,8-dilithionaphthalene.'2i 1,2,5-phosphadiborolanes have been prepared and characterized from the reactions of (2)-1,2-bis[chloro(diisopropylamino)boryl]ethane with Li,PPh and 1,2-bis[chloro(diisop- ropy1amino)boryll-1,2-diisopropyIideneethanewith LiPH,-dme; the inversion barrier at P is distinctly lower than that of related unsaturated compounds. 12j The synthesis deprotonation and ring expansion reactions of 2,3-bis(dimethylamino)-2,3-dibora-tetralin have been described'2k and the catalytic dimerization of 1,2-bis(di-isopropy1amino)-1,2-dihydr0-1,2-benzodiborete with [Pd(phthalocyanine)] led to the eight-membered tetrahydrodibenzoteraborocine (C4B4) ring with N'Pr groups on boron.' 2r Inorganic Ring Systems.-The reaction of (Et,B),O with sulfuric acid led to the crystalline cyclic sulfate EtBOB(Et)OS(O,)O whose structure has been determined by X-ray analysis; the heterocycle has also been prepared from Et,B,O on reaction with The triarylborthiins Ar,B,S (Ar = 4-MeC6H4 3-MeC6H, 2-MeC6H4 4-EtC6H, 3,5-Me,C6H,) have been prepared from the reaction of ArBBr with HgS in benzene under relfux.' 3h The substituted aryl derivatives are less air-stable than Ph,B,S and are significantly decomposed to B/O/S rings (e.g.Ar,B,S,O Ar,B,SO, and Ar,B,O,) as evidenced by mass spectrometry within minutes in air.MNDO calculations have been made on Et,B,O and Ph,B,O using both the X-ray determined and optimized geometry of these molecules.The results were compared with hypothetical 'monomeric' molecules (R-B=O) and have led to calculated energies of trimerization of ca. -200 kJ mol-'.13' The reactions of borazine with a variety of olefins (including ethylene propene 1-butene cis-and trans-2-butene 3,3,3-tri- fluoropropene styrene a-methylstyrene and 4-allylanisole) catalysed by [RhH(CO)(PPh,),] have been found to give the mono- di- and tri-B-alkyl borazines in excellent yields.' 3d The reactions of B,B',B"-trimethyl-N,N',N"-triarylborazine (aryl = Ph 4-FC,H4 and 4-MeC6H,) with [Cr(CO),] in BuO,/thf afforded com- pounds in which one aryl ring is @-bonded to a (Cr(CO),) moiety in preference to the y6-borazine ligand.'," Halide abstraction from Cl,BN(Me)PC12NPCl,N Me (struc- l3 (a) R.Koster W. Schussler D. Blaser and R. Boese Chem. Ber. 1994 127 1593; (h) M. A. Beckett P. R. Minton and 9. Werschkun J. Organomet. Chem. 1994,468,37;(c)A. Sporzynski and H. Szatylowicz,ibid. 470 31; (d) P. J. Fazen and L. G. Sneddon Organnmetallics 1994 13 2867; (e)S. Allaoud S. Conte B. Fenet B. Frange F. Robert F. Secheresse and A. Karim J. Organomet. Chem. 1994 469 59; (fl D. P. Gates R. Ziembinski A. L. Rheingold 9.S. Haggerty and I. Manners Angew. Chem. Int. Ed. Engl. 1994 33 2277; (9) 9. Kaufmann N. Metzler H. Noth and R.T. Paine Chem. Ber. 1994 127 825. M. A. Beckett Cli6i ClC2i Figure 12 Molecular structure qf the Jirst hybrid horazine-phosphazine ring [BCl(NMe)2(PCI,)2N]f as found in [BCl(NMe)2(PCl,),N][GaCl,] (Reproduced by permission from Angew.Chem. Int. Ed. Engl. 1994 33 2278) ture determined by X-ray analysis) by GaCl produced the first hybrid borazine- phosphazine ring system namely [ClBNMePCI,NPCl,N Me][GaCI,]; an X-ray crystallographic study of this compound revealed a virtually planar ring (Figure 12) with B-N bond lengths of 1.436(9) and 1.422( 10) which are similar to those found in borazines (1.43 A).13s The preparation of the Cr(CO) complex of the triphosphat- riborinane Ph,P,B,mes has been reported by reaction with [Cr(CO),(MeCN),] in acetonitrile; the complex has been characterized by NMR and by X-ray crystallogra- ~hy.',~ Multi-decker Complexes.-The photoelectron.spectra of the 30 valence electron triple -decker complexes (p-q5-C,H,B Me) [M(r5-C,H,B Me)] (M = Co Rh) have been Boron 37 R2 Ri Ri Figure 13 Iron ligand complexes of 1,4-dihydro-l,4-diboranaphthalenes (Reproduced by permission from Chem. Ber. 1994,127,1557) reported together with those of the sandwich complexes [(q5-C4H4B Me)MCp] (M = Co Rh); the reported spectra were interpreted on the basis of ab initio configuration interaction (CI)calculations carried out on model complexes involving . C,H,B H ligand~.'~" Similarly the.electronic structures of (p-C4H,B Me) [Mn(CO),] and (CXB Me)Co(p-C,H,B Me)Mn(CO) have been determined from He' PE spectra and INDO calculations in which relaxation and correlation effects have been taken into account.14' The structure and bonding of the four iron complexes shown in Figure 13 including the triple-decker complex (p-q6-C8B,H,)[FeCp] have been investigated by means of the perturbational molecular orbital theory on the basis of the Extended Hiickel calculation^.^ 4c 6 Boron-Pnictogen Species Quantum mechanical calculations predict the B-N bond length in H,NBF to be 1.68A; the previously reported experimentally determined value of 1.59A which is based on microwave spectroscopic measurements is probably too short.5a Improved syntheses of B,(NMe,), B,(NMe,), and B,(NMe,) have been reported; two of the l4 (a)I. Hyla-Kryspin R. Gleiter G. E. Herberich and M. Benard Organometallrcs 1994 13 1795; (6) R. Gleiter 1. Hyla-Kryspin and G.E.Herberich J. Organomet. Chem. 1994 478 95; (c) R. Gleiter I. Hyla-Kryspin and W. Siebert Chem. Ber. 1994 127 1557. (a) V. Jonas and G. Frenking J. Chem.SOC.,Chem. Commun. 1994,1489; (h)G. Linti D. Loderer H. Noth K. Polborn and W. Rattay Chem. Ber. 1994 127 1909; (c) D. Loderer H. Noth H. Pommerening W. Rattay and H. Schick ibid. 1605; (d) D. Dau M. Fan E.N. Duesler H. Noth and R.T. Paine Inorg. Chem. 1994 33 2151; (e) A.-C. Gaumont K. Bourumeau J.-M. Denis and P. Guenot. J. Organomet. Chem.,1994,484,9;0s.Moreton Znorg. Chim. Actu 1994,215,67;(g)T.J. Groshens and C. E. Johnson J. Organornet. Chem. 1994,480 11; (h)R. Kniep G. Gozel B. Eisenmann C. RGhr M. Asbrand and M. Kizilyalli Angew. Chem. Int. Ed. Engl. 1994 33 749. 38 M. A.Beckett terminal dimethylamino groups can be replaced by halogen to yield the qwdihalides B,(NMe,),X (X = Cl Br I) which could be further substituted at X by groups such as RO RS RHN R,P and R.'5b trans-Amination reactions of B,(NMe,) with secondary amines led to mixed tetraaminodiborane(4) compounds e.g. B,(NMe,) -,,(NR,),; B,(NC,H,,) has been characterized by an X-ray diffraction study which revealed the presence of a long B-B bond (1.75 A).' 5c Derivatives of the type R,N(Me,N)BB(NMe,)NR were more readily accessible from LiNR and B,(NMe,),Cl .' 5c Diborylphosphanes of the general formula RBClPHBR', have been prepared from the reaction of (BuiN),BP(H)Li-DME and (Pr\N)[(Me,Si),N]- BP(H)Li.DME with tmpBC1 and (Me,Si),NBCl,; the diverse dehydrohalogenation chemistry of these molecules has been studied and products such as cyclic (B2PJ 1,3-diborylated diphosphadiboretanes and acylic diphosphadiboretanes were re- ported.'5d A stable cyclic phosphine-borane adduct Bu'PHBH,CH,CH,C H has been prepared by the chemoselective complexation of allyl-t-butylphosphine with BH followed by an intramolecular anti-Markovnikov hydroboration of the adduct.5e The complex trans-[Rh(CO)X(PEt,),] (X = Br I) reacted with PH,BCl or PH,BBr in CH,Cl at 183K to yield the oxidative-addition products [Rh(CO)XH(PH,BX,)(PEt,),].' 5f Phosphinoborane compounds of the type [R,BPR;] (R = Me Et; R' = Bu',SiMe,) have been used in chemical vapour deposition studies in attempts to prepare BP thin-films on Si substrates. However all films were deficient in P (B/P = 0.5) and contained considerable carbon (C/B = 0.67-7).'5g The BPC films obtained were chemically inert and may be of interest as protective coatings.The crystal structures of MCBPO,] (M = Ca Sr) and Ba,[BP,O,,] have been undertaken.'5h 7 Boron-Chalcogen Species Kinetics of the interchange between boric acid and tetrahydroxyborate in aqueous solution of pH 8-10 at 20-52 "C have been studied by bandshape analysis of "B NMR signals; calculated activation parameters reflect a dimeric [(HO),B(p-OH)B(OH),] -transition state."" The thermodynamics of several 1:1 and 1 :2 complexes of the borate anion with bidentate ligands (1,2-ethandiol 1,2-propandiol gycolic acid lactic acid oxalic acid) have been reported.'6b Boric acid trimethyl ester has been used as a probe molecule in an IR study of the Lewis base properties of the metal oxides MgO CaO ZrO, TiO, SnO, and Sb205.16c The new compound K,Zr(BO,), which is isoelectronic and isostructural with buetschliite has been identified from a phase study of the K-Zr borate system.'6d The solid state structure of the new borate Li,Be,B(BO,) has been determined crystallographically; the structure is a dense tangle of Li- and B-centred triangles Li- and B-centred distortion 0tetrahedra and Li centred trigonal prisms."" The coordination geometry of boron in polyoxotungstates has been studied by "B MAS NMR spectroscopy; important information on the local 16 (a)K.Ishihara A. Nagasawa K. Umemoto H. Ito and K. Saito Inorg. Chem. 1994,33,3811; (b)R.Pizer and P.J. Ricatto ibid.,2402; (c)C. Li S.-F.Fu H. Zhang and Q. Xin J. Chem.SOC.,Chem. Commun. 1994 17; (d) A. Akella and D. A. Keszler Inorg. Chem. 1994 33 1554; (e)J. L. Luce K. I. Schaffers and D. A. Kesder ibid.,2453; v) A. R.Couto C. N. TrovBo J. Rocha A.M. V. Caveleiro and J. D. Pedrosa de Jesus J. Chem. Soc. Dalton Trans. 1994 2585; (g) P. Vinatier P. Graverau M. Menetrier L. Trut and A. Levasseur Actu Crystallogr. Sect. C 1994 50 1180; (h) R. Wehmschulte K. Ruhlandt-Senge M. M. Olmstead M. A. Petrie and P. P. Power J. Chem. SOC. Dalton Trans. 1994,2113; (i) M. T. Ashby and N. A. Sheshtawy Organometallics 1994 13 236. Boron 39 R a,R = IPr b,R= BU Figure 14 Reaction of WH,Cp with RBCI (Reproduced by permission from Chem.Ber. 1994 127 1613) symmetry was revealed which was not forthcoming from other techniques.' 6f The crystal structure of Li,BS, obtained by crystallizing the corresponding glass exhibits a higher symmetry than other M,B(O,S) structures such as Li,BO or TI,BS and appears to be a new member of the M,AX group of compounds.'6g The use of bulky aryl substituent groups (mes and 2,4,6-Pr;C6H,) has allowed the structural characterization of the monomeric B-S compounds mes,B(SPh) and (2,4,6-Pr\C,H,)B(SPh),; these compounds show a short B-S distance of ca. 1.808 with close alignment between B and S p-orbitals-consistant with a n-interaction; the barrier to B-S rotation obtained by variable temperature NMR studies is 18.4 and 12 kcalmol- ' respectively.'6h The barrier to rotation about the B-X bonds of coordinatively unsaturated borates and thioborates have been discussed.The lower rotational barrier in the 0 derivatives is attributed to a greater stabilization of the transition state and therefore rotational barriers do not reflect the relative strengths of the B=O and B=S n-bonds.16' 8 Boron Halide Species Quantum mechanical calculations at the MP2/TZ2P level of theory have predicted geometries and bond energies of donor-acceptor complexes of the Lewis acids BF, BCI, BH, AICI, and SO which are in good agreement with experimental gas-phase values.' 70 The zwitterions [CpWH,(q5-C,H,BRC1,)] (R = Pr' But) with exocyclic boron substituents have been isolated in 60% yield from the reactions of [CpWH,] with the Lewis acids Pr'BCl and Bu'BC1 (Figure 14); the structure of the But derivative has been determined crystallographically' 7b The dialkyl chloroborane BCIR [R = CH(SiMe,),] reacted with [NEt,][M(CN)(CO),] (M = Cr Mo W) in CH,Cl or PhMe and gave the thermally stable complexes [M(CO),(CNBR,)].The Cr derivative has a linear M-C-N-B skeleton (X-ray) consistent with the zwitterionic formulation [(CO),Cr -CN+BR,].' 7c (a)V. Jonas G. Frenking and M. T. Reetz J. Am. Chem. SOC.,1994,116,8741; (b)H. Braunschweig and T. Wagner Chem. Ber. 1994,127,1613; (c)G.Beck M. F. Lappert and P. B. Hitchcock J. Organomet. Chem. 1994,468 143.