Xavier L. R. Fontaine

X=Y-ZH compounds as potential 13-dipoles. Part 29. The iminium ion route to azomethine ylides. Reaction of cyclic secondary amines with mono- and bI- functional aldehydes

Abstract 1,2,3,4-Tetrahydro-isoquinoline and -β-carboline react with a range of mono- and bi- functional aldehydes to give azomethine ylides. The anti-dipole is formed stereospecifically or, in the case of benzaldehyde and 2-methylbenzaldehyde, stereoselectively. The effect of the structure of the aldehyde on the stereochemistry of the derived azomethine ylide is rationalised in terms of steric and electronic effects. Inter- and intra-molecular trapping of the azomethine ylides gives cycloadducts in good yield.

Polyhedral metallacarbaborane chemistry: preparation, molecular structure, and nuclear magnetic resonance investigation of [3-(η5-C5Me5)-closo-3,1,2-MC2B9H11] (M = Rh or Ir)

Reaction between Cs[nido-7,8-C2B9H11] and [{M(η5-C5Me5)Cl2}2] (M = Rh or Ir) yielded orange-yellow, air-stable crystals of [3-(η5-C5Me5)-closo-3,1,2-RhC2B9H11] [compound (2), 34%] or [3-(η5-C5Me5)-closo-3,1,2-IrC2B9H11] [compound (3), 96%] both of which were characterized by their assigned 11B and 1H n.m.r. spectra and by single-crystal X-ray diffraction analyses. Crystals of (2) were orthorhombic, space group P212121, with a = 1 081.0(2), b = 1 278.2(1), c = 1 278.4(2) pm, and Z = 4; R = 0.0197, R′ = 0.0204 for 1 756 observed reflections [I > 2.0σ(I)]. Crystals of (3) were also orthorhombic, space group P212121, with a = 1 076.3(1), b = 1 282.9(1), c = 1 292.8(2) pm, and Z = 4; R = 0.0286, R′ = 0.0307, for 1 712 observed reflections [I > 2.0σ(I)]. The n.m.r. properties of the C2B9H11 fragments of (2) and (3) are compared with the 11B and hitherto unreported 1H n.m.r. characteristics of the corresponding fragments of [3-(η5-C5H5)-closo-3,1,2-CoC2B9H11] (4), closo-1,2-C2B10H12, nido-7,8-C2B9H13, and [nido-7,8-C2B9H12]−, in order to assess any n.m.r. shielding patterns that might reveal bonding trends. The unique endo/bridging open-face hydrogen atom in [nido-7,8-C2B9H12]− is discussed in the light of its n.m.r. properties.

Novel rhodathiaborane complexes derived from [(PPh3)2RhSB9H10]

The compound [8,8-(PPh3)2-8,7-RhSB9H10], (1), has a formal closo electron count but a nido structure, exhibits unusual fluxional behaviour in solution and reacts to give both closo and nido compounds, e.g., closo-[2,3-(PPh3)2-3-(Cl)-µ-2; 3-(Cl)-2-(Ph2P[graphic omitted]H8], (2), and nido-[8,8-(PPh3)2-µ-8;9-(S2CH)-8,7-RhSB9H9], (3); the structures of (1), (2), and (3) were determined by X-ray crystallographic methods.

Two-dimensional 1H–1H COSY n.m.r. spectroscopy in polyhedral boron hydride chemistry

Two-dimensional 1H–1H COSY n.m.r. spectroscopy [with simultaneous {11B(broad band noise)} decoupling] is not subject to many of the limitations of 2D 11B–11B COSY experimentation in polyhedral boron hydride chemistry, and therefore can complement and extend it as a powerful new structural tool.

Eleven-vertex polyhedral metalladicarbaborane chemistry. Reactions of neutral nido-5,6-C2B8H12 and the [nido-6,9-C2B8H10]2− anion to give formally closo isomeric 1-(arene) and 1-(cyclopentadiene)-1,2,4- and 1,2,3-metalladicarbaundecaboranes, and some substituent chemistry. Chiral separations, and crystal and molecular structures of [5-Br-1-(η6-C6Me6)-1,2,4-RuC2B8H9] and [2-Me-1-(η5-C5Me5)-1,2,3-RhC2B8H9]

Abstract Reactions between nido -5,6-C 2 B 8 H 12 ( 1 ) and the organometallic halides [{MLCl 2 } 2 ] ( 2 ) [where {ML}={Ru(η 6 -C 6 Me 6 )} ( 2a ), {Ru(η 6 - p -MeC 6 H 4 i Pr)} ( 2b ), {Rh(η 5 -C 5 Me 5 )} ( 2c ), and {Os(η 6 - p -MeC 6 H 4 i Pr)} ( 2d )] in the presence of N , N , N ′, N ′-tetramethylnaphthalene-1,8-diamine (tmnda) in dichloromethane or chloroform have generated a series of the corresponding metalladicarbaboranes [1-L-1,2,4-MC 2 B 8 H 10 ] ( 3 , closo 11-vertex numbering system) [where {ML}={Ru(η 6 -C 6 Me 6 )} ( 3a ), {Ru(η 6 - p -MeC 6 H 4 i Pr)} ( 3b ), {Rh(η 5 -C 5 Me 5 )} ( 3c ), and {Os(η 6 - p -MeC 6 H 4 i Pr)} ( 3d )] in yields of 48–94%. The substituted species, [5-Br-1-(η 6 -C 6 Me 6 )-1,2,4-RuC 2 B 8 H 9 ] ( 5-Br-3a ) and [ 7-Br-1 -(η 6 -C 6 Me 6 )-1,2,4-RuC 2 B 8 H 9 ] ( 7-Br-3a ) have been obtained from a similar reaction involving [7-Br- nido -5,6-C 2 B 8 H 11 ] ( 7-Br-1 ) (combined yield 75%, separated by preparative HPLC). Each of the compounds 5-Br-3a and 7-Br-3a has been resolved into its enantiomers by use of chiral HPLC separation techniques. Analogous reactions between [{MLCl 2 } 2 ] ( 2 ) and the [ nido -6,9-C 2 B 8 H 10 ] 2− anion (species 4 2− ) have produced a series of the isomeric symmetrical complexes [1-L- closo -1,2,3-MC 2 B 8 H 10 ] ( 5 ) [where {ML}={Ru(η 6 -C 6 Me 6 )} ( 5a ), {Ru(η 6 - p -MeC 6 H 4 i Pr)} ( 5b ), {Rh(η 5 -C 5 Me 5 )} ( 5c ) and {Os(η 6 - p -MeC 6 H 4 i Pr)} ( 5d )]; the 2-methyl substituted compound [2-Me-1-(η 5 -C 5 Me 5 )- closo -1,2,3-RhC 2 B 8 H 9 ] ( 2-Me-5c ) has been prepared similarly using the [6-Me- nido -C 2 B 8 H 9 ] 2− anion (species 2-Me-4 2− ) as the starting dicarbaborane. All these compounds are characterised by mass spectrometry and 11 B- and 1 H-NMR spectroscopy. Single-crystal X-ray diffraction studies have been carried out on compounds 5-Br-3a and 2-Me-5c as two representative examples of the compounds in series 3 and in series 5 . The {MC 2 B 8 } clusters of compounds 3 have four-membered open faces, generating an ‘ isonido ’ geometry, whereas those of compounds 5 approximate more to the classical closo cluster geometry. Thermolyses of the {1,2,4-MC 2 B 8 } compounds 3a – 3d cleanly generate their corresponding {1,2,3-MC 2 B 8 } isomers 5a – 5d .

An unusual direct conversion of metallaboranes to metallacarbaboranes and the isolation of a novel isoarachno twelve-vertex cluster compound

Reaction of [6-(η5-C5Me5)-nido-6-RhB9H13] with RNC (R = Et, Me) in toluene at room temperature quickly gave a high yield of the bis(ligand) adducts [6,9-(RNC)2-6-(η5-C5Me5)-arachno-6-RhB9H11] which, on being heated in boiling toluene, undergo carbon incorporation to yield one- and two-carbon, eleven-vertex closo-type metallacarbaborane species rather than a reduction of RNC, whereas reaction of the isoelectronic cluster compound [6-(η6-C6Me6)-8-(OMe)-nido-6-RuB9H12] with MeNC traps an unprecedented intermediate twelve-vertex isoarachno-{RuCNB9} cluster type that has four-, five-, and six-membered open faces.

Identification of the endo, exo isomer of 6,9-(PMe2Ph)2-arachno-B10H12 by nuclear magnetic resonance spectroscopy

Reaction of PMe2Ph with nido-B10H14 results in the formation of the previously unsuspected endo,exo isomer of arachno-B10H12(PMe2Ph)2(ca. 85%) admixed with the expected exo,exo isomer (ca. 15%). Mild heating converts the endo,exo isomer into the exo,exo one. The mixture is readily analysed by multiple resonance and difference n.m.r. spectroscopy.

New complexes of rhenium-(V) or -(III) with various diphosphines or bis(diphenylphosphino)methane monoxide: crystal structure of mer-[ReCl3(dppm-PP′)(dppom-P)][dppm = Ph2PCH2PPh2, dppom = Ph2PCH2P(O)Ph2]

Treatment of [ReOCl3(AsPh3)2] or [ReOBr3(AsPh3)2] with the diphosphines, Ph2PCH2PPh2(dppm), Ph2PC(CH2)PPh2(vdpp), cis-Ph2PCHCHPPh2(dppen), or Ph2PCHMePPh2(1,1′-dppe) gave complexes of the type [ReOX3(L–L)](L–L = chelating diphosphine, X = Cl or Br), in high yield. Treatment of [ReOCl3(AsPh3)2] with an excess of dppm at 20°C caused some reduction to give a mixture of two rhenium(III) complexes [ReCl3(dppm-PP′)(dppom-P)]2a[dppom = Ph2PCH2P(O)Ph2] and [ReCl3(dppm-PP′)(dppm-P)]3a, which was difficult to separate. Treatment of [ReOCl3(AsPh3)2] with 2 mol of dppm in hot benzene gave pure 2a, whilst treatment of [ReCl3(NCMe)(PPh3)2] with 4–5 mol equivalents of dppm in hot benzene gave 3a in excellent yield. The tribromide analogue [ReBr3(dppm-PP′)(dppom-P)] was prepared by heating [ReOBr3(dppm-PP′)] with dppm. On treating [ReBr3(NCMe)(PPh3)2] with dppm, [ReBr3(dppm-PP′)(dppm-P)] was formed but this was contaminated with the isomeric salt [ReBr2(dppm-PP′)2]Br from which it could not be separated; however the NMR parameters for both components were assigned. The pure salt [ReBr2(dppm-PP′)2]BPh4 was prepared from the mixture. In their 1H NMR spectra, these rhenium(III) complexes show large paramagnetic shifts for the methylene protons of the chelated dppm and for some of the ortho-protons. Some of these resonances were assigned using two-dimensional correlation spectroscopy and nuclear Overhauser effect experiments. Crystals of complex 2a are monoclinic, space group P21/n, with a= 1147.7(4), b= 2315.5(6), c= 2069.7(6) pm, β= 91.76(3)° and Z= 4; final R factor 0.0465 for 6150 observed reflections. The structure shows octahedral co-ordination with a mer arrangement of chlorines, a chelated dppm and a monodentate dppm monoxide, with the PO group unco-ordinated.

Oxarhodaborane chemistry: the formation of [µ-9,9′-O-{5-(η5-C5Me5)-nido-5-RhB9H12}2] and [7-(η5-C5Me5)-10-(NEt3)-nido-7, 12-RhOB10H10] from [nido-(η5-C5Me5)RhB10H13Cl]

Chromatography in air on silica of the nido eleven-vertex metallaborane [(η5-C5Me5)RhB10H13Cl]2, yields the µ-9,9′-oxo-bridged bis(nido-5-rhodadecaboranyl) species [{(η5-C5Me5)RhB9H12}2O]3, whereas treatment with NEt3 before exposure to air and chromatography on silica results in the novel contiguous nido twelve-vertex oxarhodadecaborane [7-(η5-C5Me5)10-(NEt3)-nido-7,12-RhOB10H10]4.

Organo-ruthenaborane and -osmaborane cluster compounds: preparation and NMR studies of [6-(η6-C6Me6)-nido-6-MB9H13] (M = Ru, Os) and the rearranged cluster [5-(η6-C6Me6)-nido-5-RuB9H11-7-(PMe2Ph)]

Abstract Reaction of the versatile organometallaborane synthon [(η 6 -C 6 Me 6 )RuCl 2 ] 2 with arachno -[B 9 H 14 ] − affords [6-(η 6 -C 6 Me 6 )- nido -6-RuB 9 H 13 ] in 80% yield. An analogous reaction with [(η 6 -C 6 Me 6 )OsCl 2 ] 2 (here reported for the first time) gives [6-(η 6 -C 6 Me 6 )- nido -6-OsB 9 H 13 ] in 13% yield. Treatment of the nido -6-ruthenadecaborane cluster with tertiary phosphines results in rearrangement and formation of [5-(η 6 -C 6 Me 6 )- nido -5-RuB 9 H 11 -7-PR 3 ] (77% yield for PR 3  PMe 2 Ph; 54% yield for PPh 3 ). The metallaborane products are all yellow or orange-yellow air-stable crystalline compounds which have been characterized by elemental analysis, mass spectrometry, and multi-element, multiple resonance, and 2D NMR spectroscopy.