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J. CHEM. SOC. DALTON TRANS. 1986 2607Reactions of the Dirhenium(i1) Complexes [Re,X,(dppm),] (X = CI or Br,dppm = Ph,PCH,PPh,) with Isocyanides. Part 2.' The A-Frame-like Mono-isocyanide Species [Re,(p-X)(p-dppm),X,(CNR)]"+ (R = Me, But, or C,H,Me,-2,6; n = 0 or 1 ) tLori Beth Anderson, Timothy J. Barder, David Esjornson, and Richard A. Walton *Department of Chemistry, Purdue University, West Lafa yette, Indiana 47907, U.S.A.Bruce E. BurstenDepartment of Chemistry, The Ohio State University, Columbus, Ohio 432 10, U.S.A.The triply bonded complexes [ Re,X,(dppm),] (X = CI or Br, dppm = Ph,PCH,PPh,) react with RNC(R = Me, But, or C,H,Me,-2,6) to yield the monoisocyanide adducts [Re,X,(dppm),(CNR)]. Thespectroscopic properties of these species are in accord with the presence of isomers in solution.Chemical oxidation of the neutral complexes to their corresponding paramagnetic monocationsproduces a single isomer in each instance.The solid-state structure of [ Re,Cl,(dppm),(CNBut)]has been shown to be that of the A-frame-like molecule [CI,Re(p-CI) (p-dppm),ReCI(CNBut)].The retention of a Re-Re multiple bond is supported by both structural work (Re-Re = 2.30 A) anda qualitative treatment of the bonding which is consistent with the presence of a slightly weakenedtriple bond.The reactions of multiply bonded dimetal complexes with 7t-acceptor ligands, e.g. CO, NO, RNC (R = alkyl), or R'NC(R' =aryl) invariably result in the cleavage of the metal-metalb ~ n d . ~ , ~ These cleavage reactions have been observed to lead toproducts in which the resulting mononuclear fragments havesubsequently undergone non-reductive sub~titution,~,~ reduc-tive sub~titution,~-~ or simple 'adduct' formation ' ~ 3 by the7-c-acceptor ligand.In examining the related reactivity of thedirhenium(r1) complex [Re,Cl,(dppm),] (dppm = Ph,PCH,-PPh2),9.10 we have discovered that the bridging dppm ligandsconfer a remarkable stability upon the dimetal unit andprevent its disruption in the presence of an excess of a 71-acceptor ligand even under quite forcing reaction conditions.In the case of CO, both monocarbonyl and dicarbonylcomplexes can be isolated "," but an even richer chemistryensues in the case of reactions with isocyanide ligands. In thisreport we describe the nature of the 1 : l adducts that areformed between [Re,X,(dppm),] (X = Cl or Br) and RNC orR'NC.Some of these results have been the subject of apreliminary communication.Results and Discussion(a) Synthesis, Spectroscopic Properties, and Redox Be-haviour.-The triply bonded dirhenium(r1) complex [Re,-Cl,(dppm),] possesses a staggered rotational geometry." Thereactions of this complex and its bromide analogue14 withone equivalent of RNC (R = Me, But, or C,H,Me,-2,6) inacetone or toluene for ca. 30 min produce the red-brown, air-stable 1 : 1 adducts [Re,X,(dppm),(CNR)] in high yield(2 60%). These reactions, which contrast with the facilecleavage of the triple bond of [Re,X,(PR,),] (X = C1 or BrPR, = monodentate tertiary ph~sphine),~ presumably reflectthe stability of the five-membered Re-Re-PCH,P rings.Thisbehaviour resembles that seen in the reaction of[Re,Cl,(dppm), J with CO; in this instance, the formation of theI l~t N o n - U unifs employed: G = 10-4 T, B. M. = 0.927 x A m2.1 I I I I I I I 1+2-0 +1*0 0-0 -1.0 - 2.0E / V vs. Ag-AgClFigure 1. Cyclic voltammograms (scan rate 200 mV s-l at a Pt-beadelectrode) in 0.1 mol dm-3 NBu",PF,-CH2C12 of (a) [Re,Cl,(dppm),]and (b) [Re,Cl,(dppm),(CNBu')]1 : 1 adduct [Rez(p-C1)(p-dppm)2C13(CO)] precedes that of[ Re2( p-CI)(p-CO)( p-dppm),Cl,(CO)]. 1'Cyclic voltammetric measurements on solutions of thesecomplexes in 0.1 mol dm-, NBu",PF,-CH,Cl, show thepresence of two reversible one-electron processes, both of whichcorrespond to oxidations (Table 1 and Figure 1).An irreversiblereduction occurs close to the solvent limit for complexes derivedfrom the bromide [Re,Br,(dppm), 3. For the chloro-species,both processes at positive potentials are characterized by ip,c/ip,aratios of unity (or close to it) and constant ip/v* ratios for sweeprates (v) between 50 and 400 mV s-' in accord with diffusio2608 J. CHEM. soc. DALTON TRANS. 1986Table 1. Electrochemical and spectroscopic properties of [Re,X,(dppm),(CNR)]"+ (n = 0 or 1)Half-wave potentials"AI -IE+lV E,,,/V-7+ 1.31(ox) +0.32(ox)+ 1.31(ox) +0.20(0x)+ 1.27(ox) +0.31(ox)+ 1.43' +0.35(ox) - 1.63+ 1.32' + O . ~ ~ ( O X ) - 1.43+ f.30(ox) +0.3l(red)+ 1.32(ox) +0.2l(red)+ 1.43J + 0.35(red) - 1.63+ 1.30(ox) +0,34(red)'H N.m.r.; G(p.p.m.)'1 ib/nm(&/dm3 mol-' -CH,-d CH,- 31P-{1H) n.m.r.,cm-') G(p.p.m. )"666 (80), 537 (1 75) + 5.65 f + 2.79 - 6.5 1, - 7.44'''670 (150), 48 1 (630) + 5.78, + 5.60 + 0.97 - 6.39, - 11.23695 (125), 480(sh) + 5.61 +1.98 -1.04, -7.89'780 (100), 500 (1 650) +5.99, +5.66 +1.19 -4.76, -24.87k780 (200), 500 (2 050) + 5.80f + 1.44 -0.08, -28.83k1 225 (450), 795 (129,1 175 (900), 770 (1 30),IIII5 14 (900)494(1 loo)1 235 (1 300), 800 (129,505 (2 100)51 1 ( 1 250)1 260 (750), 750 (250),a Measured on 0.1 mol dm NBu",PF,-CH,Cl, solutions by the cyclic voltammetric technique (V us.Ag-AgC1). Scan rate v = 200 mV s-'.Spectra recorded in CH,Cl,. Spectra recorded in CD2C12 and referenced internally to the residual protons of the incompletely deuteriatedsolvent (6 5.35 p.p.m.).AB pattern with superimposed P-H coupling. ' Spectra recorded in a 1 : 1 mixture of CH,CI,-CD,CI,, unless otherwisestated, with aqueous 85oi, H,PO, as an external standard. Recorded in 1 : 1 CH,Cl,-CDCl, solution. AA'BB'pattern; chemical shifts are of the most intense inner components of the pattern. AA'BB' pattern; chemical shifts based upon simulated spectrum(see Figure 2).Overlapping AB pattern.values. AA'XX' pattern; chemical shifts are those of the central component of each set of peaks. ' Paramagnetic complex.Table 2. Infrared spectra of [Re,X,(dppm),(CNR)]"+ (n = 0 or 1)v(GN)/cm-', 1Complex Nujol mull CH,CI, C6H6CRe,Cl,(dppm),(CNMe)I 2 193(sh) 2 199(sh) bCRe,Cl,(dPPm),(CNBu'>l 2 103(sh) 2 133s b2 160s 2 166s2 060s 2 llO(sh)2 060m[Re2Cl4(dPPm)2(CNC6H 3Me,-2,6)1 2 060m 2 075s b1 979s 2 040(sh)2 006m2 067s 2 101s 2 097m2 066m 2 060m1995s 2 006m 1998m[Re 2 Br,(dPPm),(CNBu')l 2 097s 2 133m 2 126(sh)[Re2Br4(dppm)2(CNC,H3Me2-2,6)1 2 027m 2 041s 2 031sCRe,Cl,(dppm),(CNMe)I PF, 2 195s 2 195s bCRe,Cl,(dPPm),(CNBu')I PF, 2 149s 2 151s b~Re2Cl,(dppm),(CNC6H,Me2-2,6)]PF, 2 106s 2 108s bCRe,Br,(dPPm),(CNBu')I PF, 2 141s 2 145s ba Abbreviations: m = medium; s = strong; sh = shoulder.Limited solubility, or insolubility, in this solvent precluded recording the i.r. spectrum.control. Values of AE,, for the coupled anodic and cathodicpeaks were ca. 100 mV at v = 200 mV s-* and they increasedwith increasing sweep rate.These properties are consistent withthe electron-transfer processes being electrochemically quasi-reversible. Chemical reversibility has been demonstrated andwill be discussed later. Conductivity measurements performedon acetone solutions of these complexes (ca. 1 x mol dm-3)are in accord with their formulation as neutral species (AM = 5R-' cm2 mol-I). Their electronic absorption spectral data, whichare summarized in Table 1, reveal similarities to other ReZ4+core complexes.'6The 'H n.m.r. spectra (measured in CD,Cl,) integrate inaccord with the 1 : 1 stoicheiometry of the complexes. The reson-ances due to the methyl protons of the co-ordinated MeNC,Bu'NC, and 2,6-Me,C,H,NC ligands appear as singlets atroom temperature, while the methylene protons of the dppmligands exhibit a basic AB pattern with superimposed P-Hcoupling (JH-H 12.7-14.3, Jp-H 4.5-5.1 Hz).Data obtainedfrom the 31P-( 'H) n.m.r. spectral measurements indicate thatthe trans-bridging disposition of the dppm ligands has beenpreserved. Also, the presence of AA'BB' and AA'XX' patternsfor the chloride and bromide complexes, respectively, is indic-ative of different environments about each of the two metalcentres. The 'H and 3'P-{ 'H) n.m.r. spectral data are given iJ. CHEM. SOC. DALTON TRANS. 1986 2609-5 -106 / p.p,m.Figure 2. 3 1 P- [ 'H} N.m.r. spectrum of [Re,Cl,(dppm),(CNBu')]recorded in CH,CI,<D,CI,: (a) observed and (b) calculated. Thesimulation of this AA'BB' spectrum gave the following parameters:79.7, and JAB.= 1.2 Hz6, = -6.39, 6, = -11.23 p.p.m., J A A , = 232.3, JBB, = 212.1, JAB =Table 1, and the 3'P-{1H) spectrum of [Re,Cl,(dppm),-(CNBu')] (observed and simulated) is shown in Figure 2.The Nujol mull i.r. spectra of the monoisocyanide complexesdisplay two v(C=N) modes at frequencies characteristic of aterminally co-ordinated RNC ligand (Table 2). While thepresence of two such modes could arise from solid-state effects,the spectra of CH,Cl, or benzene solutions of the complexesalso show more than one peak (Table 2). The more solublebromo-derivatives exhibit a change in the relative intensities ofthe v(CrN) peaks with change in solvent. A similar solventdependence has been observed for the v(C=O) modes of thestructurally analogous monocarbonyl species [Re,Cl,(dppm),-(CO)]." These findings indicate that, in solution at least, thecomplexes [Re,X,(dppm),(CNR)] exist as a mixture ofisomers.These isomers can be detected on the relatively fast i.r.time-scale, while within the slower time frame of the n.m.r.technique only an averaged signal is observed. In an attempt toslow the isomerization process, a variable-temperature ' Hn.m.r. spectral study was carried out on a sample of[Re2Cl,(dppm)2(CNBu')] in CD2Cl, solution. As the temper-ature was lowered, the resonance due to the Bu'NC ligandbroadened slightly, but it never collapsed prior to reaching thelower temperature limit of - 85 "C.Based upon the preceding information we suggest that theisomers present are those represented by (I), (11), and/or (111)shown below. Isomer (I) is the species most likely to be formedfirst upon interacting [Re,X,(dppm),] with an isocyanideligand but can easily rearrange to (11) and (111) (presumablythrough very low-energy pathways) by two sequentialanticlockwise (or clockwise) motions about the planecontaining the halide and RNC ligands.In this, a single halidebridge is formed [to give (II)]; this subsequently breaks and anew bridge forms [to give (III)]. Note that in this simplemechanism the RNC remains bound to a single Re atom. ThisP-PP-Pobservation is a reasonable one since detailed n.m.r. spectralmeasurements on the analogous fluxional carbonyl complex[Re,Cl,(dppm),(l 3CO)] revealed ' ' that the CO ligand isbound to only one of the Re atoms at all times and does notbecome involved in the formation of a p-CO bridge.Oxidation of the monoisocyanide complexes using oneequivalent of NOPF, or [Fe(q 5-C5H,),]PF6 results in form-ation of the rose-coloured monocations [Re,X,(dppm),(CNR) ]-PF, ( x = c1 or Br, R = Me, But, or C,H3Me,-2,6).The electrochemistry of these oxidized species shows a processat E, ca.+ 0.3 V vs. Ag-AgC1 (corresponding to a reduction), aswell as the other redox processes which characterize the neutralRe,,+ core complexes (see Table 1). Their formulation asmonocations has been confirmed by conductivity measurementsperformed on 1 x mol dm-j acetone solutions of thecomplexes; A, = 100-120 C' cm2 mol-'.Their electronicabsorption spectral properties are given in Table 1; an intenselow-energy feature at h,,,. ca. 1200 nm is often typical ofcomplexes which contain the paramagnetic Re,5 + core.16- 'The X-band e.s.r. spectra of [Re2Cl,(dpprn),(CNR)]PF,,measured as dichloromethane glasses, exhibit a broad complexsignal between 500 and 4000 G which is centred at g = 2.85.The observed magnetic moments, determined by the Evansmethod,lg are consistent with the complexes possessing oneunpaired electron, pObs. z 1.6 B.M.Oxidation of the monoisocyanide complexes by one electronappears to generate a single isomer. The i.r. spectra, recorded asNujol mulls or dichloromethane solutions, display a singlesharp band assigned to a terminally co-ordinated isocyanideligand (Table 2).The frequency is shifted to higherwavenumbers relative to v(CrN) of the neutral complex, asexpected with the decrease in n-backbonding from Re2'+ toRNC. Reduction back to the neutral species (using an acetonesolution of cobaltocene) regenerates the same mixture ofisomers that was present originally (as monitored by i.r.spectroscopy ).(b) Structural Considerations.-While single crystals of[Re,Cl,(dppm),(CNBu')] of sufficient quality to justify an X-ray crystal-structure analysis could be grown from dichloro-methane solution, subsequent structure refinement wasfrustrated by a disorder problem. Nonetheless, the structure wasestablished to be that of the A-frame-like molecule (l), which isisomer (111) discussed in the preceding section.The disorderinvolves the C1 and Bu'NC ligands trans to the bridging C1ligand (the basic structural details are presented in theExperimental section). The structure closely resembles that ofthe monocarbonyl derivative [Re,Cl,(dppm),(CO)], where 2610 J. CHEM. SOC. DALTON TRANS. 1986similar disorder is present but the structure solution has proventractable. A Re-Re distance of 2.30(1) 8, is clearly indicative ofthe retention of a multiple bond, a point which is discussedfurther in section (c). The comparable bond distance in triplybonded [Re,Cl,(dppm),] is 2.234(3) 8 , . l 0 Other distances ofnote in (1) are Re-P 2.47(1), Re-Cl, 2.56(2), and Re-CI, 2.52(2)8,. The angle at the bridging C1 ligand is ca. 54" which compareswith that (55") in the structure of [Re,Cl,(dppm),(CO)].' Asfar as we can ascertain, the crystal(s) selected for the structuresolution were representative of the bulk.This signifies that atleast in the solid-state [Re,Cl,(dppm),(CNBu')] (and probablythe MeNC and 2,6-Me2C,H,NC analogues) exists primarily asthe A-frame-like isomer (111).(c) A Consideration of the Metal-Metal Bonding in [Re,CI,-(dppm),L] (L = CNR or CO).-The extent of metal-metalbonding in A-frame molecules containing only weakly bondingor non-bonding interactions between the metal centres has beenaddressed by Hoffman and Hoffmann.,' The Re-Re bonds in(C6)Yi5 are substantially shorter than the M-M bonds in otherchloro-bridged A-frame structures. For example, the Rh atomsin [Rh2(p-C1)(p-dppm),(C0),] + are at a non-bonding distanceof 3.152 The M-p-CI-M angles in these complexes (54-55" in the Re systems; 82" in the Rh system) indicate that thebridging atom confers a negligible effect on the M-M bondlength.It is thus apparent that much of the Re-Re multiplebond character of [Re,Cl,(dppm),] is preserved upon theaddition of CNR or CO. In an effort to explain the multiplemetal-metal bonding within this unusual structural unit, weoffer the following qualitative scheme.We start with [Re,X,(dppm),] as a prototypical d5-d5dimer containing a 02n4626*2 Re-Re triple bond., We assume,for convenience, that the molecule is in an eclipsed conform-ation, an assumption that does not affect the Re-Re bonding.We now allow two weak 0 donors L to ligate in the axialpositions of the molecule.The effect of this ligation will be aslight weakening of the Re-Re bond due to the donation of asmall amount of electron density into the o* orbital. We willneglect this effect and assume that [Re,X,(dppm),L,] possessesa 02n:4826*2 triple bond, An A-frame structure can be formedfrom this molecule by rotation of the two ReX,P,L fragmentsabout the P-Re-P axis in a disrotatory fashion and eliminationof one of the X groups, thereby yielding [Re,(p-X)(p-dppm),X,L,] + (Scheme). The bridging X- ligand acts as a four-electron donor whereas all the others are two-electron donors. Ifthe metal orbitals are allowed to rotate along with the Re atoms,then we preserve the same orbitals for Re-Re bonding, thoughreferenced to a new co-ordinate system (Scheme).We willassume a rotation of 30" which generates an A-frame with aRe-p-X-Re angle of 60", close to that observed crystallo-graphically.In order to describe the metal-metal interactions in the A-frame (denoted d, n', 6', and S*') in terms of diatomic 0, n, 6,and 6* interactions, the rotated d orbitals must be referenced tothe unrotated co-ordinate system. The transformation betweenCRe ( C1>(~-dppm)2C13(CNR)1 and ~Re2(~-C1)(~-dppm)2c13-P-P P A D l+Scheme.the two systems, for a rotation of 30°, is given by x ' = k''? x +the rotated d orbitals can be expressed in terms of the unrotatedorbitals as shown below and thus the Re-Re interactions in-2-, 1, y' = y, and z' = -i.x + 3 z .Using this transformationthe A-frame, referred to standard diatomic interactions, aregiven below.dz2 -dz2 = g 0 + & ~ + & 6d,, -dxz = & o + $ ~ + & 6d xq' - d XY = b n : + $ 6dyz - dyz = 2 n: + 4 6Within this model, the Re-Re triple bond is preserved uponformation of the A-frame, although we may envisage it as a 'bent'triple bond. In terms of diatomic interactions the 0 ' ~ 7 ~ ' ~ 6 ' ~ 6 * ' ~triple bond becomes a o%f6%*h*: triple bond.The effects on the metal-metal bond upon rotation of[Re,X,(dppm), L,] into the A-frame [ Re2@-X)( p-dppm),-X,L2]+ are therefore the transfer of nominally 4 e from nbonding to 6 bonding orbitals and 4 e from 6 antibonding to n:antibonding orbitals. Both of these will tend to weaken theRe-Re triple bond somewhat,Although some very broad assumptions have been made, e.g.the n-backbonding abilities of RNC and CO have beenneglected, this model is in accord with the experimentalobservations. The Re-Re bond length of 2.30 - 2.35 8, in the A-frame systems is only slightly longer than those in othercomplexes containing 'standard diatomic' Re-Re triplebonds.2,'0,22 Also, the ready accessibility of two one-electronoxidations in the A-frame, as measured by cyclic voltammetry,is consistent with the highest energy electrons residing in Re-Reantibonding orbitals. Quantitative molecular-orbital calcul-ations aimed at substantiating the qualitative model presentedhere will be performed in the near future.(d) Concluding Remarks.-The neutral multiple bondedcomplexes [Re,X,(dppm),(CNR)] (X = C1 or Br; R = Me,But, or 2,6-Me,C,H3), appear to exist as isomers in solutionalthough in the solid state we have definitive evidence only forthe A-frame-like isomer (111).A single isomer is obtained uponoxidizing these complexes to their monocations (isolated astheir PF, - salts). The isolation of [Re,X,(dppm),(CNR)Jprovides evidence in support of our earlier suggestion that thereaction of [Re,Cl,(dppm),] with nitriles R'CN to givJ. CHEM. SOC.. DALTON TRANS. 1986 261 1[Re,Cl,(dppm),(NCR'),]+ proceeds via the A-frame-likespecies [ Re,Cl,(dppm),(NCR')].23 These monoisocyanideadducts provide only the second series of multiply bondeddimetal complexes that contain isocyanide ligands and whichhave been stabilized towards metal-metal bond cleavage. Theprevious examples are the complexes [Re,X,(L-L),(CNR)]PF,(X = C1 or Br; L-L = Ph,PCH,CH,PPh, or Ph,AsCH,-CH,PPh,; R = Pr' or BU').'''~ The reactivity of the newcomplexes towards nitrile ligands and carbon monoxide iscurrently under investigation and will be reported in due course.ExperimentalStarting Materials.-The dirhenium(I1) complex [Re,Cl,-(dppm),] was prepared, according to the reported method,from [Re,CI,( PBu",),] and dppm,' while the bromo-derivative[Re,Br,(dppm),] was synthesized from the reaction between[Re,Br,( PPr",), J and dppm in refluxing benzene, as described inthe literature. The bromide complex was recrystallized fromCH,Cl,-Et20 prior to use. Pertinent n.m.r.spectral data for thiscomplex are as follows: 'H n.m.r. (['H,]acetone) 6 5.65 p.p.m.(quintet, -CH,- of dppm), ,lP-{ 'H) n.m.r. (CH2Cl,-CD2C1,) 6+5.60 p.p.m. (singlet). The MeNC and Bu'NC ligands wereprepared using standard literature p r o c e d u r e ~ , ~ ~ . ~ ~ while 2,6-Me,C,H,NC was purchased from Fluka Chemicals and usedwithout further purification. The oxidant [Fe(q 5-C,H,),]PF6was prepared using the reported method with minormodification^.^^ The solvents used in the preparation of thecomplexes were of commercial grade and were thoroughlydeoxygenated prior to use. All reactions were performed under anitrogen atmosphere using standard vacuum-line techniques.Monoisocyan ide Complexes.-( i) [Re ,CI,( d p pm) ,( CNB u') J0.5CH2CI,. In a typical reaction, [Re,Cl,(dppm),] (0.20 g,0.16 mmol) was dissolved in acetone ( 5 cm3).The purplesolution immediately turned red-brown upon addition of 1 molequiv. of Bu'NC (0.0165 cm3, 0.16 mmol). The reaction mixturewas stirred at room temperature for 30 rnin until a red-brownsolid precipitated. The solid was recrystallized by dissolving it indichloromethane (5 cm3) and slowly adding diethyl ether (30cm3). The desired product, which precipitated upon standing,was collected, washed with diethyl ether, and dried in vacuo;yield 0.20 g, 94% (Found: C, 46.6; H, 3.9; C1, 12.8.C,,.,H,,C15NP,Re, requires C, 47.3; H, 3.9; Cl, 12.6%). Thepresence of half a molecule of CH,CI, was verified by measuringthe 'H n.m.r.spectrum in CDCl,.The following complexes were prepared by using a similarprocedure: [Re,Br,(dppm),(CNBu')], yield 60% (Found: C,42.1; H, 4.2; Br, 20.9. C,,H,,Br,NP,Re, requires C, 42.8; H, 3.5;Br, 20.7%); [Re,Cl,(dppm),(CNMe)], yield 80% (Found: C,46.95; H, 3.9. CS,H,,C14NP,Re2 requires C, 47.1; H, 3.95%);and [Re,Cl,(dppm),(CNC6H3Me2-2,6)]~0.5CH2C12, yield 912,(Found: C, 48.5; H, 3.9; C1, 11.9. C,,,,H,,Cl,NP,Re, requiresC, 49.0; H, 3.75; Cl, 12.2%).(ii) [Re,Br,(dppm),(CNC,H3Me,-2,6)]. The synthesis ofthis complex involved the dropwise addition of a toluenesolution (3 cm3) of 2,6-Me2C,H,NC (0.0074 g, 0.056 mmol) to atoluene solution (5 cm') of [Re,Br,(dppm),] (0.083 g, 0.055mmol). The resulting red solution was stirred for 5 min and thevolume of solution then reduced to ca.4 cm3 under a stream ofgaseous nitrogen. Diethyl ether was added to precipitate thedesired product. It was filtered off, washed with diethyl ether,and dried in vacuo; yield 0.064 g, 71% (Found: C, 45.4; H, 3.7.C,,H,,Br,NP,Re, requires C, 44.5; H, 3.4%).Oxidat ion of Monoisocyanide Complexes.-[ Re,CI,( dppm), -(CNBu')]PF,. A quantity of [Re2Cl,(dppm),(CNBut)] (0.10 g,0.073 mmol) was dissolved in dichloromethane ( 5 cm3). To thissolution was added 1.1 mol equiv. of NOPF, (0.014 g, 0.08mmol). Evolution of NO gas, accompanied by a change incolour from red-brown to red, occurred within 15 min of stirringthe solution at room temperature. The stirring was continuedfor an additional 15 min, then the reaction mixture was filteredto remove any unreacted NOPF,.The rose-coloured productwas precipitated from the filtrate by the addition of diethyl ether(25 cm3). It was collected, washed with diethyl ether, and driedin uacuo; yield 0.083 g, 75% (Found: C, 43.7; H, 3.9; Cl, 9.2.C,,H5,C1,F,NP,Re, requires C, 43.7; H, 3.5; C1, 9.4%). Thisoxidation can also be achieved using [Fe(q5-C,H5),JPF, as theoxidant in dichloromethane solution.The following complexes were prepared in an analogousmanner: [Re,Br,(dppm),(CNBu')]PF,, yield 78% (Found: C,38.8; H, 3.6. C5,H,,Br,F,NP5Re, requires C, 39.1; H, 3.2%);[Re,Cl4(dppm),(CNC,H3Me2-2,6)]PF6, yield 70% (Found: C,44.7; H, 3.6; C1, 9.0. C,,H,,Cl,F,NP5Re, requires C, 45.4; H,3.4; C1, 9.1%); and [Re,Cl,(dppm),(CNMe)]PF,, yield 70%(Found: C, 42.1; H, 3.8.C5,H,,C1,F,NP,Re, requires C, 42.5;H, 3.2%).Reduction of [Re2Cl,(dpprn),(CNBut)]PF6. A quantity of[Re,Cl,(dppm)2(CNBu')]PF, (0.10 g, 0.066 mmol) wasdissolved in acetone (5 cm3) and treated with 1 mol equiv. ofcobaltocene (0.012 g, 0.066 mmol). The reaction mixture wasstirred at room temperature for 20 min. After this time, theneutral dirhenium species had precipitated from the solution. Itwas collected and recrystallized by dissolving in dichloro-methane and slowly adding diethyl ether. It was filtered off,washed with diethyl ether, and dried in vacuo; yield 0.065 g, 72%.The identity of the reduced complex was confirmed through acomparison of its electrochemical and spectroscopic propertieswith those of an authentic sample.Physical Measurements.-1.r. spectra were recorded as Nujolmulls or solutions in CH,Cl, or benzene using an IBMInstruments IR/32 Fourier-transform (4 8 M O O cm-')spectrometer. Electronic absorption spectra were recorded onIBM Instruments 9 420 u.v.-visible (900-200 nm) and Cary 17(2 O G 9 0 0 nm) spectrophotometers.Electrochemical experi-ments were carried out by using a Bioanalytical Systems Inc.model CV- 1 A instrument on dichloromethane solutions con-taining 0.1 mol dm-, NBu",PF, as supporting electrolyte.€+ values [(E,,, + EP,J2] were referenced to the Ag-AgClelectrode and are uncorrected for junction potentials. Under thesame experimental conditions the ferrocenium-ferrocene couplehas E, = + 0.47 V vs.Ag-AgC1. ' P-I'H) N.m.r. spectra wererecorded on a Varian XL-200 spectrometer operated at 80.98MHz, with an internal deuterium lock and using aqueous 85%H,PO, as an external standard. Positive chemical shifts weremeasured downfield from H,PO,. 'H N.m.r. spectra were alsorecorded on a Varian XL-200 spectrometer. Resonances werereferenced internally to the residual protons in the incompletelydeuteriated solvent. Conductivities were measured on anIndustrial Instruments Inc. model RC 16B2 conductivitybridge. X-Band e.s.r. spectra of dichloromethane solutions wererecorded at ca. -160°C with the use of a Varian E-109spectrometer. Magnetic susceptibility measurements were doneby the Evans method" on dichloromethane solutions of thecomplexes using a Varian XL-200 spectrometer.Microanalyses were performed by Dr.H. D. Lee of thePurdue University microanalytical laboratory.Preparation of SingZe Crystals of [ Re,Cl,(dppm),(CNBu')].-Dark red crystals of [Re,CI,(dppm),(CNBu')] were obtainedby dissolving a 0.1 g sample of the complex in dichloromethane(2 cm3) in a 5-mm n.m.r. tube and layering with diethyi ether(1.5 cm3). Crystals deposited on the side of the tube within 5 d.Because of a disorder problem, the structure solution did no2612 J. CHEM. SOC. DALTON TRANS. 1986proceed to a stage sufficient to warrant publication of the fullstructural details. However, the basic crystallographic details(at 25 "C) are as follows: monoclinic, s ace group P2,, a =5 980(9) A3, 2 = 4, D, = 1.524 g ~ m - ~ , p(Mo-K,) = 45.1 cm-'.Conventional heavy-atom methods were used in the structuresolution which was terminated at the stage R(F) = 0.13 andR'(F) = 0.15 for 6 720 observed reflections having Fo2 > 30-(I;,'). A total of 7435 unique reflections were collected(2 < 20 < 50') on an Enraf-Nonius CAD-4 diffractometerusing graphite-monochromated Mo-K, radiation. Furtherdetails of the data set, and the structure solution and refinementmay be obtained from Dr.P. E. Fanwick of this Department.15.007(7), b = 15.091(7), c = 26.282(14) x , p = 90.22(2)", U =AcknowledgementsWe thank the National Science Foundation for researchsupport (to R. A. W.) and Professor W. R. Robinson and Dr. P.E. Fanwick for their efforts in solving the X-ray crystalstructure.B. E. B. acknowledges a Teacher-Scholar grant fromthe Camille and Henry Dreyfus Foundation and a Fellowshipfrom the Alfred P. Sloan Foundation.References1 Part 1, L. B. Anderson, T. J. Barder, and R. A. Walton, Inorg.Chem., 1985, 24, 1421.2 F. A. Cotton and R. A. Walton, 'Multiple Bonds Between MetalAtoms,' Wiley and Sons, New York, 1982, and refs. therein.3 R. A. Walton, in 'Reactivity of Metal-Metal Bonds,' ed. M. H.Chisholm, American Chemical Society, Washington, D. C.; A CSSymp. Ser., 1981, 155, p. 207 and refs. therein.4 J. D. Allison, T. E. Wood, R. E. Wild, and R. A. Walton, Inorg. Chem.,1982, 21, 3540.5 C. J. Cameron, S. M. Tetrick, and R. A. Walton, Organometallics,1984. 3, 240.6 D. D. Klendworth, W. W. Welters, 111, and R. A. Walton,Organometallics, 1982, 1, 336.7 C. A. Hertzer, R. E. Myers, P. Brant, and R. A. Walton, Znorg. Chem.,1978, 17, 2383.8 T. Nimry, M. A. Urbancic, and R. A. Walton, Inorg. Chem., 1979,18,691.9 T. J. Barder, F. A. Cotton, D. Lewis, W. Schwotzer, S. M. Tetrick,and R. A. Walton, J. Am. Chem. SOC., 1984, 106, 2882.10 T. J. Barder, F. A. Cotton, K. R. Dunbar, G. L. Powell, W.Schwotzer, and R. A. Walton, Inorg. Chem., 1985, 24, 2550.11 F. A. Cotton, L. M. Daniels, K. R. Dunbar, L. R. Falvello, S. M.Tetrick, and R. A. Walton, J. Am. Chem. Soc., 1985, 107, 3524.12 F. A. Cotton, K. R. Dunbar, L. R. Falvello, and R. A. Walton, Inorg.Chem., 1985,24,4180.13 T. J. Barder, D. Powell, and R. A. Walton, J. Chem. Soc., Chem.Commun., 1985, 550.14 J. R. Ebner, D. R. Tyler, and R. A. Walton, Inorg. Chem., 1976,15,833.15 F. A. Cotton, K. R. Dunbar, L. R. Falvello, A. C. Price, W.16 L. B. Anderson, S. M. Tetrick, and R. A. Walton, J. Chem. SOC.,17 J. R. Ebner and R. A. Walton, Inorg. Chim. Acta, 1975, 14, L45.18 B. E. Bursten, F. A. Cotton, P. E. Fanwick, G. G. Stanley, and R. A.19 D. F. Evans, J. Chem. SOC., 1959, 2003.20 D. M. Hoffman and R. Hoffmann, Inorg. Chem., 1981, 20, 3543.21 M. Cowie and S. K. Dwight, Inorg. Chem., 1979, 18, 2700.22 T. J. Barder, F. A. Cotton, L. R. Falvello, and R. A. Walton, Znnorg.23 J. Casanova, R. E. Schuster, and N. D. Werner, J. Chem. SOC., 1963,24 W. D. Weber, G. B. Gokel, and I. K. Ugi, Angew. Chem. Znt. Ed. Engl.,25 D. N. Hendrickson, Y. S. Sohn, and H. B. Gray, Inorg. Chem., 1971,Schwotzer, and R. A. Walton, J. Am. Chem Soc., in the press.Dalton Trans., 1986, 55.Walton, J. Am. Chem. SOC., 1983, 105, 2606.Chem., 1985, 24, 1258.4280.1972, 11, 530.10, 1559.Received 30th December 1985; Paper 51227

ISSN:1477-9226    

DOI:10.1039/DT9860002607

出版商:RSC    

年代:1986

数据来源: RSC