摘要:

J.CHEM. SOC. DALTON TRANS. 1983 261 3Amidino-complexes of Rhenium. Bidentate NN'- and ortho-MetallatedDerivativesJ. Andrew Clark and Melvyn Kilner *Department of Chemistry, The University of Durham, South Road, Durham DHI 3LE[Re(CO),(R'NC(R)NR'}] complexes ( I ; R = Me or Ph; R' = Ph or c~H4Me-p)~ containing delocalisedbidentate N N'-chelated amidino-groups, have been prepared by reactions of (i) [(Re( CO),X},](X = CI or Br) with R'N(Li)C(R)NR', (ii) [Re(CO),(R'NC(R)NHR')X] with LiBu", (iii) [Re,(CO),,]with R'NHC(R)NR', and ( i v ) by decarbonylation of [Re(CO),(CON(R')C(R)NR'}] complexes.Triphenylphosphine displaces CO from (I) to form [Re(CO),(PPh,){R'NC(R)NR'}] (IT), which are moreconveniently prepared by the reactions of [ Re(CO),L'Br] (L' = PPh3 or AsPh,) withamidines in refluxing toluene.This reaction stops at the intermediate compound[Re(CO),(PPh,)(R'NC(R)N(Me)R')Br] when a NNN'-trisubstituted amidine is used. Related complexes[ Re(CO),( PPh3){ R'NC( R)NHR'}Br] are formed when (11) are treated with hydrobromic acid.[Re(CO),X] (X = CI or Br) and [{Re(CO),Br}2] react with amidines to form o-metallated[Re(CO),{R4NC(R)NHC6H3R"-p}{R'NC(R)NHR8}] (R = H, R' = Ph; R" = H; R = Me or Ph, R' =C,H,Me-p, R" = Me; R = Me or Ph, R' = Ph, R" = H) complexes which contain a six-memberedo-metallated ring. Benzamidines (R = Ph) produce in addition an isomeric complex in whicho-metallation of the R substituent occurs to give complexes having five-membered o-metallated rings.Intermediate [ Re(CO),{ R'NC( R) N H R'},X] complexes were isolated for R' = C,H,Me-p, R = Me, andX = Cl or Br.A lI3-proton-shift mechanism for the o-metallation reaction is eliminated by theformation of the complex [Re( CO) ,( R'N C( Me) N ( Me)C6H,Me-p}{ R'N C( Me) N (Me) R'}](R' = C,H,Me-p) from R'N(Me)C(Me)NR'. Reaction schemes are suggested for the course of thereactions, and structures for the new complexes are proposed on the basis of spectroscopic data.The amidino-group although known to act as a monoden-tate one-electron ligand to transition metals,' bonds in themajority of its complexes as a "'-chelate 2-9 or NN'-bridging lo-'' three-electron donor. Symmetrical chelateamidino-groups (I) have been characterised in a variety of dif-ferent complexes including [ Mo(q5-CsHs)(CO),{PhNC(Me)N-Ph)] and [Pd{p-MeC61-t4NC(Me)NC6H4Me-p)2],5 though un-symmetrical chelate groups (11), as found in [TaMeCl,-{PriNC(Me)NPri},],ll are less well documented.Spectro-scopic data lead to the assignment of symmetrical NN'-bonded amidino-groups to a range of molybdenum, tung-ten,^*^*'-^ manganese,2*6 rhenium,6 platinum, and palladium '*complexes and related triazine complexes. "'-Bridgingamidino-groups (111) and (IV) occur in many complexes suchR'NIM \C-R'N'IR' RlI I1I11 I Vas [MO,(P~NC(P~)NP~),],~* [Re2(PhNC(Ph)NPh}2C14],19 and[CU,{P~NC(P~)NP~}~],'~ as well as in dinuclear complexes,e.g. [{Me2NCH2(C6H3)CH2NMe2)Pt{N(C6H4Me-p)CH-NC6H4Me-p)AgBr]," having an amidino-group bridgingbetween two different metals, structure (IV).Diarylamidines- -R'IRo - metallatedRL' MeL2 MeL3 PhL4 PhL5 HRNN'-chelatedMLR 'Phc 6 H4Me-pPhc 6 H@-pPhRR "HMeHM eHRM261 4 J. CHEM. SOC. DALTON TRANS. 1983Table 1. Analytical data, melting points, and yields for NN-bidentate [Re(CO)4L] and [Re(C0)3L’L] (L’ = PPh3 or AsPh3) complexesAnalysis (‘A) *Complex[Re(C0)4( PhNC(Ph)NPh}]7 H N Yield (%) M.p. (“C) C148 48.5 2.55 4.85 21[Re(C0)4(p-MeC6H4NC( Ph)NC6H4 Me-p}] 114[Re(CO),{ PhNC( Me)NPh}] 146[ Re(CO),{p-MeC6H4NC( Me)NC6H4Me-p}] 1 40(48.5) (2.65) (4.9)49.9 3.25 4.65 20(50.2) (3.2) (4.7)42.6 2.4 5.5 20(42.6) (2.55) (5.5)45.7 3.25 5.3 18[ Re(CO),( PPh3)(p-MeC6H4NC(Me)NGH4Me-p) 1 (44.8)196 (decornp.) 57.8(3.2)4.2(5.25)3.65 31 ~~(57.8) (4.15) (3.65)196 (decornp.) 56.7 3.8 3.8 45(56.7) (3.75) (3.75)(60.7) (4.1) (3.35)(59.8) (3.75) (3 * 5 )(54.6) (3.95) (3.45)[Re(CO)3(PPh3){p-MeC6H4NC( Ph)NC6H4Me-p}] 190 (decornp.) 61.6 4.2 3.35 38[Re(CO),(PPh3){ PhNC(Ph)NPh}] 192 (decornp.) 59.9 3.85 3.65 42[Re(CO)3(AsPh3){p-MeC6H4NC(Me)NGH41he-p}] 185 (decomp.) 54.7 4.0 3.5 13* Calculated values are in parentheses.Table 2.1.r. carbonyl stretching frequencies for NN’-bidentate [Re(CO),L] and [Re(C0)3L’L] (L’ = PPh3 or AsPh,) complexesComplex[ Re(CO),{ PhNC(Ph)NPh}][ Re(C0)4{ p-MeC6H4NC(Ph)NC6H4 M e-p}][Re(CO),(PhNC( Me)NPh}][ Re(CO),{ p-MeC6H4NC(Me)NC6H4 Me-p } I[Re(CO),(PPh3){PhNC(Me)NPh}1[ Re(C0),(PPh3){p-MeC6H4NC( Me)NC,H4Me-p}][Re(C0)3( PPh3){ PhNC( Ph)NPh}][ Re(C0)3( PPh3){ p-MeC6H4NC( Ph)NC,H 4Me-p}]MediumCH2ClzNujolCH2C12NujolC H z aNujolCHzCl2NujolCH2CIzNujolCHZCIZNujolCH2CIzNujolCH2CIzNujolO( CO)/cm-l2 117w, 2 005vs, 1 981vs, 1 947vs2 IlOw, 1 995vs, 1973vs, 1918vs2 103w, 2 002vs, 1 947vs, 1 930vs2 106w, 2 OOOvs, 1 978vs, 1 911vs2 114w, 1 998vs, 1976vs, 1 933vs2 1 low, 1 992vs, 1 978vs, 1 940vs2 1 low, 2 OOOvs, 1 976vs, 1 932vs2 OOOw, 1 992vs, 1 977vs, 1 938vs2019vs, 1912vs, 1888vs2016vs, 1909vs, 1885vs2018vs, 1914vs, 1882vs2 012vs, 1 907vs, 1 883vs2 020vs, 1 917vs, 1 888vs2 022vs, 1 91 lvs, 1 894vs2 021vs, 1 917vs, 1 890vs2 019vs, 1 91 8vs, 1 907vs1899vs, 1 887vsact also as three-electron donor groups as a result of o-metal-lation of an aryl substituent.Six-membered metallocycles (V)are usually formed, as illustrated by[Pd(q5-C5HS){p-MeC6H4NC(Me)NHC6H3Me-p)l.5*18As an extension to our work on amidino-complexes of man-ganese,’ we have investigated the reactions of amidines withvarious rhenium carbonyl complexes. Derivatives of the type[Re(CO),{CON(R’)C(R)NR’}] and [Re(CO),{ R’NC(R)-NHR’}X] (X = Cl or Br) ’’ will be reported elsewhere, and theformation and characterisation of a range of NN’-chelatedand o-metallated amidine complexes (see below) are the sub-jects of this paper.* The “’-chelate complexes are analogousto the manganese derivatives,2 and to the formamidine com-plexes [Re(CO)4(R’NCHNR’)] reported by Abel and Skit-tralL6 Distinct differences between manganese and rheniumoccur with respect to o-metallation.Such reactions have notbeen reported for manganese though it is found here to be acommon reaction for rhenium. The only other o-metallationI I* Throughout this paper a bridge bond through L indicates orrho-metallation.reactions of amidines reported previously occur for palladiumand platinum c ~ m p l e x e s , ~ ~ , ’ ~ and rnerc~ry.’~Results and DiscussionA. [ Re(CO),L] (HL = Amidine) Complexes.-Complexes ofthe type [Re(C0)4L] were prepared by the reaction of [{Re-(CO),X),] (X = C1 or Br) with lithiodiaryl-acetamidines and-bemamidines in monoglyme (1,2-dimethoxyethane) solution.They were bright yellow air-stable solids (m.p. ca. 140 “C)which formed yellow air-stable solutions in organic solvents.The complexes were identical with the decarbonylationproducts of [Re(CO),(COL)] (ref.22), and i.r. spectroscopicmonitoring of the reactions indicated that although theyield of recovered material was only ca. 20%, the complexeswere formed in solution in very good yield. Two additionalproducts, [Re(CO),(HL)X] and an o-metallated complexI I[ Re(CO),L( HL)] were formed, and separation proved difficultbecause of similar solubilities. Pure material was obtainedusing fractional crystallisation methods and the seedinJ. CHEM. SOC. DALTON TRANS. 1983 261 5Table 3.1.r. absorptions associated with the delocalised "'-chelate amidino-groupsComplex[ Re(CO),{ PhNC( Me)NPh}][ Re(C0)4{p-MeC6H4NC( Me)NC,H4Me-p}][ Re(CO),(PhNC( Ph)NPh}][ Re(CO),{p-MeC6H4NC(Ph)NC6H4Me-p}][ Re(CO),( PPh,){ PhNC( Me)NPh}][ Re(CO),(PPh3){p-MeC6H4NC( Me)NC,H,Me-p)][ Re(CO)3(PPh3){ PhNC(Ph)NPh >][ Re(CO),(PPh,){p- MeC6H4NC( Ph)NC6H4 M e-p}]11111111111111111.r. absorptions (cm-')590m, 1575w, 1 495s, 1475s412s, 1364m, 1312w, 1297w606w, 1 570vw, 1 502s, 1490s475s, 1412s, 1368m, 1315w, 1293w590m, 1 570w, 1 525w, 1490s475 (sh), 1 425s, 1 365w, 1 273w606w, 1 569w, 1 502s, 1432s365w, 1298w, 1272w590w, 1 500m, 1475m, 1 429w410m, 1218m600vw, 1 500m, 1 475m, 1429wm413m, 1408w, 1358wm, I 288w, I 222m588w, 1 576w, 1495m, 1485m, 1 468m430s, 1375m, 1312w, 1275w, 1212w603w, 1565w, 1 500m, 1465m425s, 1 408w, 1 310w, 1 295w, 1 268wFigure 1.Carbon-13 n.m.r.data (CDCI,) for [Re(CO),(PhNC-(Ph)NPh}]: 1 = I ' = 145.97, 2 = 2' = 123.74, 3 = 3' = 128.55,4 = 4' = 122.96, 5 = 165.00, 6 = 123.68, 7 = 128.94, 8 = 129.98,9 = 132.71, 10 = 10' = 189.77, 11 = 11' = 186.78 p.p.m.technique. Excessive loss through retention of the complexeson silica gel and alumina columns prevented their use.Attempts to find alternative preparative routes to avoidthese difficult product separations led firstly to the use oftoluene and hexane as alternative reaction solvents, then to thereactions of [Re(CO),(HL)X] (X = Cl or Br) with n-butyl-lithium, and finally to the direct reactions of dirhenium deca-carbonyl with amidines using U.V. irradiation. All reactionsled to the desired complex, but in the last case the yield wasvery small.Using toluene or hexane, mixtures of products wereagain obtained and the yields were not significantly different.The similarity between the solution i.r. spectra of [Re(CO)*L]and [Re(CO),(HL)X] (X = C1 or Br) in monoglyme orhydrocarbon solvents made monitoring of the LiBu" reactionmost difficult, and because the reaction produced the 0-R I'M NHk /N=C/ \0C 0c\ I/yeOC c0R" 'RV V I VIImetallated complex as a by-product, this preparative routeprovided no advantages over the route using [(Re(CO),X),].Yields were slightly better, though this advantage was off-setby the necessary presynthesis of [Re(CO)*(HL)X] complexes.Formulation of the complexes as [Re(CO),L] is based onanalytical data (Table l), i.r.spectra (Table 2), and massspectrometry. The pattern, position, and relative intensitiesof the carbonyl stretching absorptions in the i.r. spectrum areconsistent with a cis-disubstituted octahedral structure. In themass spectrometer all the complexes exhibited molecular ions,and fragmentation occurred by successive loss of four carbonylgroups before fragmentation of the amidino-ligand. The for-mulation of the complex and the known adherence of com-plexes of this type to the 18-electron rule imply that theamidino-group is a three-electron bidentate ligand. Of thepossible types of chelate bonding, uiz. n-type (VI), o,n-type(VII), symmetrical o,o-type (I) and unsymmetrical o,o-type(11), previous experience favours the symmetrical o,o-type (I)which is found both for [Pd{PhNC(Ph)NPh),] and [Mo-(q5-C,H5)(CO),(PhNC( Me)NPh}].' This is confirmed for thediphenylbenzamidino-complex by the I3C n.m.r.spectrum,data from which is given in Figure 1. The symmetrical natureof the amidino-group is indicated by the equivalence of thecorresponding aryl carbon atoms of the N-substituents andthe occurrence of only two signals due to carbonyl carbons.No appreciable change occurred in the spectrum over a rangeof temperatures down to -60 "C, eliminating the possibilityof equivalence due to rapid interchange of the bonding mode.Though the n-type bonding mode (VI) cannot be eliminatedby the n.m.r. data it is unlikely to occur in preference tobonding through donor nitrogen atoms, as shown notably forthe palladium complex [Pd(PhNC(Ph)NPh}2].5Some characteristic i.r.absorptions for the amidino-groupare recorded in Table 3. Compared with the spectra of thefree amidines the predominantly asymmetric NCN stretchingvibration at ca. 1 600 cm-' absorbs ca. 20 cm-I lower in thecomplex. The symmetric stretch is similarly lowered with theabsorption now occurring at ca. 1 500 cm-l. These changes aresimilar to those observed for other rhenium-amidine com-plexes.The formation of [Re(C0)4L] complexes from [ (Re(CO),-X},] (X = C1 or Br) and lithioamidines is thought not to takeplace via attack at a carbonyl group as there is no evidence ofcarbamoyls being formed. Two routes are possible for thereaction, as shown in Scheme 1. It is not possible to predictwhich of the reaction routes is followed.The formation of[Re(CO),L] from the reaction of [Re(C0)4(HL)X] with n-butyl-lithium can also take place via two similar routes in26160OC\OC’0CReC0I /I‘Scheme 1. Reaction schemes for the formation of [Re(C0)4-{ R’NC(R)NR}] complexes (X = C1 or Br)volving elimination of LiX in the first or second stages of thereaction (Scheme 2). Interestingly, the reaction of [Re(CO)4-L] with HBr forming ~is-[Re(C0)~(HL)Brl can be regardedas the reverse reaction. Protonation of the nitrogen leads tothe formation of a monodentate amidine ligand and a vacantco-ordination site at the metal. Nucleophilic attack by abromide ion leads to the product. Preliminary work demon-strates that this type of reaction can be achieved using otheraqueous acids, e.g.nitric acid.B. [Re(CO),L‘L] (HL = Amidine, L’ = PPh3 or AsPh,)Complexes.-Reaction of [Re(CO)4L] complexes with ami-dines in refluxing monoglyme or toluene is unusual in that1 Ithe products, [Re(CO),L(HL)] contain an o-metallatedamidine group (see section C). With PPh3 in refluxing toluene,however, only a simple substitution reaction occurs to form[Re(C0)3(PPh3)L], with no evidence of o-metallation. Theamidine retains its bidentate attachment to the metal, and it isa carbonyl group which is displaced. The phosphine andrelated arsine complexes are more easily obtained from thereactions between [Re(C0)4L’Br] complexes (L’ = PPh, orAsPh,) and amidines in refluxing toluene.Hydrogen bromideis eliminated and captured by the excess amidine as HL*HBr,and displacement of carbon monoxide results from the co-ordinated amidino-group becoming bidentate. The reactionproceeds in moderate yield (about 40%), the products beingwhite, air-stable, crystalline solids with melting points around195 “C. Only the facial isomer is observed, having three car-bony1 stretching frequencies at ca. 2 020,l 900, and 1 890 cm-’.The analogous reaction using the NNN’-trisubstituted amidinep-MeC6H4N(Me)C(Me)NC6H4Me-p (HL’”) is very slow andthe tricarbonyl product, [Re(CO),(PPh,)(HL”)Br], which isisolated represents the intermediate stage in the formation of[Re(CO),(PPh,)L] complexes from [ Re(CO),(PPh,)Br] andHL. Elimination of MeBr is not achieved in the same way aselimination of HBr, and the reaction consequently stops atthe substitution stage.For the complexes [Re(CO),(PPh,)L] where L = L2 andL4, ‘H n.m.r.spectroscopy showed the two p-tolyl methylgroups to be magnetically equivalent, and the skeletal C-CH,signal to consist of a doublet ( J = 4 Hz). The splitting isattributed to long-range P-H coupling, since the coupling isJ. CHEM. SOC. DALTON TRANS.R‘ R’N N(CO),Red ‘C-R (C0i4ReJ \C-R\ /Bun NHR‘\ / X NHR’LiEun -HBu” 1 -HBU” 1R’ R‘Scheme 2. Reaction of [Re(CO)4{R’NC(R)NHR‘}X] (X =Br) with LiBu”1983C1 orTable 4. Analytical data for the o-metallated complexesPh, Me, or H; R’ = Ph or C6H4Me-p; R” = H or Me; R”’ =H or Me) and also for [Re(CO)3(R’NC(Me)NHR’}2X] (R’ =C6H4Me-p, X = C1 or Br)1 I [Re(CO)~(R‘NC(R)N(R”’)GH3R’’-p){R’NC( R)N( R”’)R’}] (R =Analysis (%) aComplex C H N[Re(CO)3L1(HL1)] 54.1 4.15 8.1I I (54.0) (3.9) (8.15)[Re(CO)3L2(HLz)] 56.5 7.2 4.7m (56.4) (7.5) (4.7)[Re(C0),L3(HL3)]Isomer I 61 .O 3.9 6.8Isomer I1 62.0 4.05 7.0n (60.5) (3.8) (6.9)[Re(C0),L4(HL4)]Isomer I 62.1 4.5 6.45Isomer I1 62.4 4.85 6.4n (62.6) (4.9) (6.4)[ Re(C0),LS(HLS)] 52.6 3.5 8.5(52.6) (3.5) (8.45)[Re(CO),(HL2),C1] 53.8 4.6 7.2[Re(CO)dHL2)2Brl 47.0 4.35 6.8(53.7) (4.7) (7.15)n (46.6) (4.1) (6.8)[ Re(CO),L*”(H L’”)] 57.6 5.3 7.45(57.4) (5.05) (7.25)Calculated values are in parentheses.CI, 4.60 (4.55%). Br,10.0 (9.70%).absent from the spectra of the corresponding arsine com-plexes.Substantial amounts (up to 20% yield) of trans-[Re(CO),-(PPh,),Br] form in the reactions of [Re(C0)4(PPh,)Br] withamidines and represents the reaction of displaced PPh, withthe starting material.The fate of the rhenium complex fromwhich the triphenylphosphine was lost was not discoveredthough a probable product, o-metallated [Re(CO),L(HL)],was not detected. Interestingly, no o-metallated amidino-groups were formed although they form readily when amidinesolutions are refluxed with [Re(C0)4(HL)Br] and otherrhenium complexes. Three explanations are possible, (i)[Re(C0)3(PPh3)L] complexes are both thermally stable (m.p.ca. 190 “C) and stable towards reaction with other reagents;(ii) o-metallated amidines may have more steric interactionswith a cis-PPh3 than a NN’-chelated amidino-group, and (iii)7 J.CHEM. SOC. DALTON TRANS. 1983 2617Table 5. 1.r. carbonyl and N-H stretching frequencies for [Re(CO)3(HL)2X] (X = C1 or Br) and o-metallated [Re(CO)3L(HL)]complexesMediumNujolNujolCHzClzCHzClzCHzClzNujolNujolCH2CliCHzClZNujolCHZC12NujolNujolNujolNujolCHzClzCH2C12G(CO)/cm-‘2 012vs, 1 890vs br2002vs, 1 894vs, 1 879vs2 015vs, 1 887vs br2002vs, 1 887vs, 1 878vs2018vs, 1 898vs, 1885vs2010vs, 1 880vs br2 016vs, 1 912vs, 1 873vs2012vs, 1895vs, 1882vs2 OlOvs, 1 890vs, 1877vs2 016vs, 1 916vs, 1 868vs2020vs, 188% br2015vs, 1900vs, 1878vs2 018vs, 1 900vs, 1 875vs2 018vs, 1 900vs br2 022vs, 1 895vs br2022vs, 1 904vs, 1 888vs2 020vs, 1 905vs, 1 8WvsO( N-H)/cm-’3 343w3 342m3 348w3 346m3 341w3 340m3 341w3 340w3 340m3 332w3 365w3 348m--3 210w, 3 150w3 210wsteric interactions of a chelate o-metallated transition stateprevent this process occurring.Since molecular models showthat the o-metallated group interacts sterically with adjacentgroups to a lesser extent than the NN’-chelated group, thefirst explanation seems the most plausible. Further, o-metal-lated [Re(CO),L(HL)] reacts with PPh3 to produce theNN-chelated complex [Re(CO)3(PPh3)L].Preliminary work suggests that fac-[Re(CO),(PPh,)(HL)X]complexes can be produced by reaction of [Re(C0)3(PPh3)L]with a range of protic acids i.e. HCl, HBr, HI, HF, HN03,HC02H, and PhOH.C. o-Metallated Amidine Complexes.-When [Re(CO),X](X = CI or Br) and [(Re(CO)4Br}z] are refluxed in mono-glyme with amidines, the complexes [Re(C0)3L(HL)](L = L*-L5 and L2“) are formed in good yield.Thecomplexes were identified by elemental analysis (Table4) and mass spectrometry, and confirmed by i.r. (Table5 ) and n.m.r. data. In order that the complexes fulfilthe 18-electron rule, the amidino-groups must contribute atotal of five electrons to the rhenium, which is most likelyachieved by one amidino-group acting as a three-electrondonor and the other as a two-electron donor. The occurrenceof a medium-intensity sharp i.r. absorption at ca. 3 340 cm-’for each of the complexes (except for [Re(C0)3L2m-(HL2”)]} indicates the presence of a N-H group. Moreover,the unusually sharp nature of this band and its relatively highfrequency indicates that it arises from an o-metallatedamidino-group, as found in the palladium complex[ Pd(q ’-CS H,) ( p - MeC,H4NC( Me)NHC,H,Me-p}] .’ Relatedcomplexes are well documented for rhenium and, indeed,o-metallation is a common reaction of rhenium complexeswith nitrogen ligands having aryl substituent~.~~ The sharpness,intensity, and high frequency of v(NH) have been found to bediagnostic of this type of attachment.The three strong v(C0)absorptions observed in the i.r. are consistent with a facialisomer as shown in Figure 2.o-Metallated six-membered-ring structures are assigned tothe acetamidine (L’) and formamidine (L5) complexes pre-pared.Similarly, one of the isomeric products obtained usingr--1m1 IR “R- C\NHR‘NHR‘/NR‘/ RCFigure 2. (a) Structure of the o-metallated complex[Re(CO),{ R’NC( R)NHCsH3R”-p}{ R’NC(R)NHR’}] (R” = H orCH,); (b) structure of the o-metallated complexI II I [Re(CO),{ R’NC(C,H,)NHR’}{ R’NC(R)NHR’}]HL3 (isomer I) and the major product (isomer I ) obtainedusing HL4 are assigned related structures. However, forbenzamidines (HL’ and HL4) a second o-metallated productis possible, having a five-membered ring incorporating theC-C,H, substituent [see Figure 2(6)]. Because of the similarityin the carbonyl stretching frequencies for all the complexesexcept isomer I1 for the benzamidino (L’ and L4) complexes,they are assigned the same structure.Isomers I1 in commonwith the other complexes have the distinctive N-H absorp-tion. However, the three carbonyl stretching frequencies arenoticeably different to those of the other o-metallated com-plexes, particularly in the position of two absorption binds.Thus a slightly different structure seems probable, and theavailable data are consistent with the presence of a five-membered-ring system as shown in Figure 2(b). The diphenyl-benzarnidino (L’) derivative was not detected in the reactionbetween [Re(CO),Br] and HL’, although such a complex wasisolated as a minor product of the reaction of [Re(CO),L3]with HL3 (ref. 22).Hydrogen-1 n.m.r. spectra of all the p-tolyl o-metallatedcomplexes, both five- and six-membered rings, consist of twomethyl resonances attributable to the p-toIyl methyl groups i261 8 J.CHEM. SOC. DALTON TRANS. 1983( a )( b lQ-y,FR\Br\Re* NPhPh-HBr___)- B r -4R\PhMe q-I\/FR Re+ NPh\IPh q-F\N=C-RIMe-H+ -PhScheme 3. Possible reaction schemes leading to o-metallation of amidinesthe ratio 3 : 1. It is concluded that the two p-tolyl methylgroups of the monodentate amidine and thep-tolyl methyl ofthe o-metallated amidino-group remote from the metal havecoincidental overlap of resonances. The unique methylresonance is assigned to the methyl group on the o-metallatedaromatic ring. The acetamidine derivatives show two moremethyl resonances arising from the different environments ofthe skeletal C-CH, groups.In reactions involving HL2 intermediate complexes of thetype [Re(CO),(HL'),X] (X = CI or Br) were obtained in smallyield.Related complexes for other amidines were not detected.The complexes showed three strong carbonyl stretching fre-quencies in the i.r. spectrum consistent with a facial tricar-carbonyl complex, and showed (for X = C1) the expected twomethyl resonances (ratio 2 : 1) in the 'H n.m.r. spectrum. Theparent ion [Re(CO)3(HL2)2CI]+ in the mass spectrum gave aweak peak, the predominant peaks arising from o-metallated[Re(CO),L'(HL')], the thermolysis product formed in theion source. Interestingly, in attempting to separate the lasttwo complexes in the preparative work to obtain a pure sampleof the latter, heating the mixture to 190 "C was effective inremoving the chloro-complex as a contaminant.Elimination ofHCI (or HBr) appears important in the reaction scheme lead-ing to o-metallated complexes.With regard to the mechanism of the o-metallation reac-tions, another important reaction is that of the NNN'-trisub-stituted amidine p-MeC6H4N(Me)C(Me)NC6H4Me-p with[Re(CO)SBr] which leads to the o-metallated compound-[Re(C0),L2"(HL2")]. Following the failure of this amidineto produce an o-metallated complex with [PdC1412-, in con-trast with the "'-disubstituted amidine, it was suggested *8that the N-H group was an important feature which wouldallow a 1,3-shift of an o-hydrogen to an adjacent nitrogen (seeScheme 3). Though this type of mechanism is not entirelyeliminated by the o-metallation of the trisubstituted amidine,such a process will produce a quaternary nitrogen prior toproton loss [Scheme 3, reaction (b)].For these amidines protonloss may be assisted by the nitrogen lone pair in a 1,3-proton-transfer reaction. Such base promoted reactions are welldoc~mented.'~ Current thinking favours an intramoleculararomatic substitution mimicking classical electrophilic arom-atic substitutions, as illustrated in Schemes 3 and 4, and wesuggest that the process involves the presynthesis of [Re(CO),-(HL),Br], isolated or detected as an intermediate in some ofthe reactions. The following steps, the elimination of Br-,the formation of a metal-arene complex, and the formation ofa carbonium ion prior to final elimination of H+, are similarOCOCtRe(CO15Brl + 2HLR?R "R'011OCOCScheme 4.Formation of' o-metallated [Re(CO),L(HL)]to those proposed for the formation of other o-metallatedfor example a five-membered o-metallated productfrom [PdCl4l2 - and diarylhydrazines.26 The reversible natureof the o-metallated amidine reaction was demonstrated by theaction of hydrobromic acid on o-metallated [Re(C0)3L2-(HL2)] in methanol. This caused the formation of [Re(CO)3-(HL2),Br], and indicates the route by which the other rheniumcomplexes of this type may be synthesised.There are other recorded examples of reverse o-metallationreactions. For example the loss of hydrogen and the formationof an o-metallated product from [RuHCI{P(OPh),),] can bereversed using hydrogen gas, and this type of reaction can beused to exchange ortho aromatic protons with D2.25 Also, thereaction of [PdX2{P(OR)3}2] to form the palladated complex[Pd(o-C,H40P(OR)2}{P(OR)3}X] (X = C1, Br, or I; R = Phor C6H4CI-p) can be reversed by treating the latter complexeswith hydrogen chloride in dichl~romethane.~~J.CHEM. SOC. DALTON TRANS. 1983R "2619Route A t [ H + l T1 Route BR( i v ) - [H'I IScheme 5. Possible mechanism for the interchange of amidino-group bonding from "'-chelate to o-metallate typeThe formation of some five-membered o-metallated ringcomplexes when benzamidines were used represents an altern-ative reaction route available to these materials. A similarmechanism for the formation is envisaged.Interestingly,although five-membered-ring systems are generally favouredover six-membered rings (minimal ring strain being thedetermining factor), six-membered rings are favoured overfive-membered rings for the benzamidine complexes in termsof the yields of product formed. Though it is conceivable thatthe six-membered rings may be stabilised by a substantialdegree of delocalisation of n electrons (pseudo-aromatic 6n-electron system), this is not realised in practice for other com-plexes. The X-ray crystal structure of the complex[~d(~5-C5HS){~-MeC6H4NC(Me)NH~6H3Me-~}]75 for ex-ample, showed a puckered, non-delocalised r'ing systemhaving a variety of C-N bond distances.o-Metallated complexes are the ultimate products of mostreactions of rhenium carbonyl halides or amidine complexeswith excess amidines. [Re(CO),X], [{Re(CO),Br},], and[Re(CO),(HL)X] (X = C1 or Br) in the presence of excessamidine and at a suitably high temperature all form o-metallated [Re(C0)3L( HL)] complexes.Similarly, [Re-(CO),L] and [Re(CO)4(COL)] react with amidines in refluxingtoluene to form the same complexes. A similar reaction routeto Scheme 4 is envisaged, the initial step being the ligandsubstitution of carbonyl by amidine and protonation (frommthe solvent or other amidine species) of one nitrogen of thechelated amidine (Scheme 5 , route A). n-Arene co-ordination,followed by electrophilic substitution of the ring by the metalwould regenerate the proton. Alternatively, a 1,3-proton-switch reaction (Scheme 5 , route B) could occur.The extent to which steric crowding influences the o-metallation reactions is of interest.It is found that suchreactions occur only when two amidines are attached to themetal, and not when a combination of amidine and PPh3or AsPh3 groups are present. Molecular models suggestthat for both types of complexes, [Re(CO),L(HL>] and '[Re(CO),L(PPh,)], strong interactions between ligandsoccur but only in certain configurations. However, it is likelythat steric interactions in the intermediates, viz. [Re(C0)3-(HL),X] and [Re(CO),(PPh3)(HL)X] are more important. Thebis(amidine) complex shows a much greater degree of stericinteraction than the amidine-phosphine complex, causingone of the aryl groups to approach closely to the metal.It ismost likely that the different steric interactions are responsiblefor the presence of an o-metallated group in [Re(CO)3L(HL)]but a "'-chelate group in the corresponding phosphinecomplex [Re(C0)3(PPh3)L].An additional factor to be taken into consideration for the[Re(CO),L] reaction with amidines is the relative stability ofthe "'-chelate versus o-metallated chelate complexes.Indeed the "'-chelate group would be the straightforward2620 J. CHEM. SOC. DALTON TRANS. 1983NHR'IOC , JR'Scheme 6. Possible later stages in the reaction of o-metallated[Re(C0)3L(HL)] with PPh3rnderivative envisaged, and it seems likely that the strong elec-tron donation, which would result in a complex [Re(C0)3L-(HL)] from (J donation by three nitrogen atoms, would pro-duce an unacceptably high electron density on the metal.This could be relieved by detachment of one nitrogen fromthe metal, followed by the subsequent o-metallation reaction.Thus in such circumstances formation of a metal-carbon bondwould not be unexpected. Such an interpretation is supportedby the numerous [Re(CO)3LzX] complexes which form withL' = amine, phosphine, and arsine, etc., and which fail toundergo further displacement of carbon monoxide (seebelow) .24-2co[Re(CO)5Br] + RNH2 ___t [Re(C0)3(NH2R)2Br]The change in bonding of the amidine which results wheno-metallated [Re(CO),L(HL)] reacts with PPh3 is moredifficult to explain.Since reaction of the complex with hydro-bromic acid reverses the o-metallation reaction, we envisagean acid-catalysed reversal of stages (iii) and (iv) of route A(Scheme 5) in the reaction with PPh3.The reversal of stage (ii)will be favoured by the presence of PPh3. Steric crowding ofthe facially substituted [Re(C0)3(PPh3)(HL)2]+ intermediate(Scheme 6) would cause the displacement of a monodentateamidine group by the unco-ordinated nitrogen of the secondamidine group, and loss of a proton would generate the NN'-amidinochelate complex [Re(CO),(PPh,)L].Experiment a1The amidines, [Re(CO)SX], [{Re(CO),X)J, and [Re(CO),L'X](X = C1 or Br; L' = PPh3 or AsPh,) were prepared by pub-lished method^.^^*^^ All solvents were dried and rigorously de-gassed before use. Alumina used was by Woelm (neutral,activity 111). n-Butyl-lithium in hexane solution (3.5 mol dm-3)was supplied by Alfa.All reactions were carried out under anatmosphere of nitrogen.1.r. spectra were recorded on a Perkin-Elmer 456 spectro-meter, proton n.m.r. spectra at 60 MHz on a Varian E.M.360L spectrometer, and I3C n.m.r. spectra on a BrukerHX90E spectrometer modified for Fourier-transform oper-ation using a Nicolet B.N.C.12 computer. N.m.r. samples weredissolved in deuteriochloroform and SiMe4 was employed asan internal reference. Raman spectra of solid samples wererecorded on a Cary 82 spectrometer utilising a Spectrophysics164 argon-ion laser source.Carbon, hydrogen, and nitrogen contents were determinedusing a Perkin-Elmer 240 Elemental Analyser.Chlorine andbromine analyses were obtained by combustion of the com-plexes in oxygen followed by potentiometric titration of thehalide ions.Reaction of [ {Re(C0)4Br}2] with PhN(Li)C(Ph)NPh.-n-Butyl-lithium (3.46 mol dmA3 in hexane) was added to afrozen (- 196 "C) solution of NN'-diphenylbenzamidine(0.941 g, 3.46 mmol) in monoglyme (40 cm3). The mixturewas allowed to warm to room temperature, and then stirredfor 15 min. The lithio-reagent was then transferred by syringeonto solid [(Re(C0)4Br}z] (1.31 g, 1.73 mmol) and the mixturestirred. After 30 min the white suspension had dissolved, anda clear yellow solution formed. The solution was evaporatedin vacuo to dryness, small additions of diethyl ether being usedto prevent gum formation.After extraction with toluene(25 cm3), the solution was filtered through alumina (1 in-thick)before reduction in volume and cooling to -10 "C. Whitecrystals of [Re(C0),(HL3)Br] separated. Addition of hexaneto the mother-liquor and cooling gave yellow crystals of[Re(C0),L3] which were recrystallised from toluene solution.The peak at highest m/e value in the mass spectrum of theyellow crystals was due to the parent ion at m/e 570, Daughterions corresponded to the stepwise loss of the four carbonylgroups. Metastable peaks were not observed.Reaction of [{Re(CO)4Br}2] with p-MeC6H4N(Li)C(Ph)-NC,H,Me-p.-The reaction conditions and procedure wereidentical to those described above. The crude product con-tained [Re(C0)4L4], [Re(CO)4(HL4)Br], and o-metallated[Re(CO),L4(HL4)] which were identified by i.r.spectroscopy.This crude product was recrystallised from toluene-hexanegiving yellow crystals of [Re(CO),L4]. 'H N.m.r. (CDCI,): 6(number of protons in parentheses) 6.95 (2), 6.74 (2), 6.61(4), 6.45 (5), 2.18 p.p.m. (6).1---,Reaction of [{Re(C0)4Cl}2] with PhN(Li)C(Ph)NPh andp-MeC6H4N(Li)C(Ph)=Nc6H4 Me-9.-The reaction conditionsand procedure were identical to those described above forLiL3. The products, [Re(C0),L3] and [Re(C0),L4] respect-ively, were identified by i.r. spectroscopy.Reaction of [{Re(C0)4C1}2] with PhN(Li)C( Me)NPh.-Thereaction conditions and procedures were identical to thosedescribed above for LiL3. The initial crude product con-tained [Re(C0)4L1], [Re(CO),(HL')CI], and o-metallated[Re(CO),L'(HL')], identified by i.r.spectroscopy. Latersamples were yellow crystals of [Re(CO),L'] which were re-crystallised twice from hexane solution. 'H N.m.r. (CDCI,) :6 7.25, 7.13, 6.93, 6.80 (lo), 2.07 p.p.m. (3).-Reaction of [{ Re(CO),Cl},] with p-MeC,H,N(Li)C( Me)N-C6H4Me-p.-The reaction conditions and procedure wereidentical to those described above for LiL3. The product wasrecrystallised twice from hexane giving yellow crystals. 'HN.m.r. (CDCI,): 6 6.87, 6.73 (S), 2.30 (6), 2.03 p.p.m. (3).Reaction of [Rez(CO) with p-MeC6H4NHC(Ph)NC6H4-Me-p.-[Re2(CO),,] (0.788 g, 1.21 mmol) and HL4 (0.725 g,2.42 mmol) were dissolved in toluene (20 cm3), and the solu-tion refluxed for 12 h. Although the solution became darkbrown no changes occurred in the v(C0) stretching frequencyregion of the i.r.spectrum. U.V. irradiation over 8 h caused afurther darkening of the colour, and eventual loss of v(C0J . CHEM. SOC. DALTON TRANS. 1983 262 1absorptions. Evaporation of the reaction mixture to small bulk( 5 cm3), addition of diethyl ether (2 cm3), and cooling to- 10 "C gave a mustard coloured precipitate. Recrystallisationfrom dichloromethane-hexane solution gave a very smallquantity of [Re(C0),L4].Decarbonylution of [Re(C0)4(COL)] Complexes.-Thispreparative route will be described in a following paper.22Reaction of [Re( CO ),( H L3) Br ] with n-Bu ty Z- Zith ium . -n-Butyl-lithium (1.14 mmol) in hexane solution was added to afrozen solution of [Re(C0),(HL3)Br] (0.743 g, 1.14 mmol) inmonoglyme (40 cm3) at - 196 "C.The mixture was warmed toambient temperature, stirred for 30 min, then the solvent wasremoved from the yellow solution in vacuo. The residue wasextracted with toluene (40 cm3), the solution filtered, reducedin volume (to 5 cm3), then cooled to -10 "C. Yellow crystalsof [Re(CO),L3] were produced (yield 0.402 g, 62%). Furthercrystals produced from the solution were identified as o-me tallated [ Re(CO),L3( HL3)].r - IReaction of [ Re(C0)4(HL4)Br] with n-Butyl-Zithium.-Reaction procedure and conditions were identical to thosedescribed above. [Re(C0),L4] was obtained in 60% yield,but two other crystalline products were produced, andwere identified as the two isomers of o-metallated[Re( C0),i4( HL4)].Reactions of [Re(CO),(HL)Br] (HL = HL' or HL') withn-Buryf-lithium.-Reaction conditions and procedure wereidentical to those described previously.The products were[Re(CO),L] and o-metallated [Re(C0)3L(HL)] (L = L' orL2), the [Re(C0)4L] complexes being obtained in 30 and 24%yield respectively.-Reactions of [Re(CO),(HL)Cl] with n-Butyf-lithium.-Thecomplexes formed were identical to those described for reac-tions involving the bromo-complex, and in similar yields.Reaction of [Re(C0),L3] with Hydrobromic Acid.-[Re-(C0),L3] (0.100 g, 1.75 mmol) was suspended in methanol(10 cm3) and hydrobromic acid (0.3 cm3, 47%, 1.75 mmol)added slowly dropwise. The solid which changed colour fromyellow to white was separated by filtration, washed withmethanol, and dried under vacuum.The product was identi-fied by i.r. spectroscopy as [Re(CO),(HL3)Br].Muss Spectra of [Re(C0)4L] Complexes.-Parent ions werethe highest m/e fragments detected for all [Re(CO),L] com-plexes. Daughter ions corresponded to stepwise loss of thefour carbonyl groups, and preceded the fragmentation of theamidino-groups. No metastable peaks were observed.Reaction of [Re(CO),(PPh,)Br] with HL2.-The complex(0.500 g, 0.78 mmol) and HL2 (0.371 g, 1.56 mmol) were dis-solved in toluene (40 cm3) and the mixture refluxed for 4 h.The solvent was evaporated in uacuo to 10 cm3, diethyl ether(10 cm3) added, and the mixture cooled to -10 "C. A whiteprecipitate of the amidine hydrobromide separated and wasidentified by 'H n.m.r.and i.r. spectroscopy. Pentane (10 cm3)was added to the mother-liquor, and further cooling producedhard, white crystals of [Re(CO),(PPh,),Br] (0.1 51 8). Removalof the solvent from the mother-liquor in uacuo, followed byextraction of the residue with carbon tetrachloride (10 cm3),and cooling the solution, produced white [Re(C0),(PPh,)L2].Yield 0.19 g, 31%. 'H N.m.r. (CDCl,): 6 7.20 (7), 7.10 (2),6.92 (l), 6.60 (l), 6.47 (l), 2.31 (s, 6 ) , 1.45 p.p.m. (d, 3, J = 4Hz). Mass spectrum: peak at highest mle value due to parention [187Re(CO)3(PPh3)L2] + at m/e 770; the fragmentationsshown below were observed; no metastable ions wereobserved.- co -co -co -PPh3 - 742 - 714 - 686 - t.f[ReL2] +m/e 770 m]e 424I- 508 ___)_ 480 __t 452 --PPh3 -co -co -coI[Re(C0),(PPh,)L2] +Reactions of [Re(CO),(PPh,)Br] with HL', HL4, and HL3.-The reaction conditions and procedure were identical to thosedescribed above for HL2.The products were off-white solids,[Re(C0),(PPh3)L], formed in the following yields: L = L1(4579, L4 (38%), L3 (42%). 'H N.m.r. (CDCI,): 6 [Re(CO),-(PPh,)L1], 7.13 (17), 6.75 (4), 6.61 (4), 1.62 p.p.m. (d, 3,J = 4 Hz); [Re(C0)3(PPh3)L4], 7.40 (l), 7.25 (4), 7.17 (3),6.87 (4), 6.63 (l), 6.30 (l), 2.19 p.p.m. (3). Mass spectrum:the parent ions were observed for L = L4 and L3 at m/e 832and 804 respectively. As described above for [Re(CO),-(PPh,)L*], two fragmentation routes are observed, involvingeither three successive losses of carbonyl groups followed bytriphenylphosphine to form [ReL] +, or initial loss of triphenyl-phosphine followed by the successive loss of three carbonylgroups.Most of the ion current arose from the former process.For [Re(C0),(PPh3)L4], metastable peaks at m* 721 and 696were assigned to [Re(C0),(PPh3)L4] + * [Re(CO)(PPh,)-L4] + and [Re(CO)(PPh3)L4]+ -+ [Re(PPh3)L4] + fragment-ations respectively. For [Re(C0),(PPh3)L3] two metastablepeaks at m* 721 and 693 are assigned to these same processes,and m* 749 to [Re(C0),(PPh3)L3] + - [Re(C0),(PPh3)L3] + .Similar mass spectrum fragmentation patterns were observedfor [Re(C0)3(PPh3)L'], all daughter ions being detectedalthough the parent ion at m/e 742 was not observed. Againthe initial loss of a carbonyl group was the favoured route.Reaction of [Re(CO),(AsPh,)Br] with p-MeC,H,NHC-(Me)NC6H4Me-p.-[(Re(CO)4Br)2] (0.500 g, 0.66 mmol) andtriphenylarsine (0.405 g, 1.32 mmol) suspended in carbontetrachloride (40 cm3) were heated at 50 "C for 2.5 h.An i.r.spectrum showed that [Re(CO),(AsPh,)Br] had formed ingood yield. The aniidine (0.62 g, 2.64 mmol) was added andthe mixture refluxed for 3 h. Removal of the solvent in uucuo,followed by solvent extraction of the residue with toluene(4 cm3), filtering the solution, and cooling to -- 10 "C yieldeda white precipitate of the amidine hydrobromide, which wasidentified by i.r. and 'H n.m.r. spectroscopy. Further coolingand reduction in volume of the mother-liquor yielded a whitesolid, which after recrystallisation from dichloromethane-hexane, was identified as [Re(C0)3(AsPh3)L2].'H N.m.r.(CDCI,): 6 7.07 (m), 2.31 (s, 2), 1.63 p.p.m. (s, 1). Massspectrum: parent ion [187Re(C0)3(AsPh3)L2] + at m/e 814 wasthe highest mass peak, and fragmentation patterns wereidentical to those of the phosphine derivatives (see below).-co -co -co -- AsPh3 - 786 __t 758 __t 730 - tf[ReL2] +mle 814 m/e 4241- 508 __t 480 __t 452 -- AsPh3 -co -co -- co1[Re(C0),(AsPh3)L2] +Reaction of [Re(CO),(PPh,)Br] with p-MeC6H4N(Me)C-(Me)NC,H,Me-p.-[Re(Co)J(PPh,)Br] (0.200 g, 0 . 3 1 mmol)and HL'm (0.079 g, 0.31 mmol) were dissolved in toluen2622 J . CHEM. SOC. DALTON TRANS. 1983(10 cm'), and the mixture refluxed for 21 h. The solution wasfiltered from a white precipitate, which contained neitheramidine nor carbonyl groups, and after reducing to small bulk(2 cm3) and cooling, trans-[Re(CO)3(PPh3)zBr] separated.Attempts to obtain the main product from the solutionusing a variety of solvents and conditions failed, though thei.r.solution spectrum [in CH2C12: v(C0) 2020s and 1904s,br cm-'1 suggests strongly that the complex is [Re(CO)3-( PPh3)(HL2m)Br].Reactions of [Re(CO),L] (L = L3 or L2) with PPh3.-[Re(C0)4L] (0.21 mmol) and PPh3 (0.055 g, 0.21 mmol) weredissolved in toluene (20 cm3) and the mixture refluxed for 2 h.After evaporation to small bulk (10 cm3), cooling and additionof pentane (5 cm3), white crystals of [Re(C0)3(PPh3)L] com-plexes were obtained. Yield for L = L3, 0.12 g (67%).Reaction of [Re(C0)4L3] with PhNHC(Ph)NPh.-Thecomplex (0.205 g, 0.36 mmol) and HL3 (0.098 g, 0.36 mmol)were dissolved in toluene (12 cm3), and the solution refluxedfor 4 h.After evaporation to small bulk (3 cm') in vacuo, afew drops of hexane were added and the mixture cooled to- 10 "C. Yellow crystals of o-metallated [Re(C0),L3(HL3)]were produced (yield 0.20 g, 66%). This product is describedfully later in the Experimental section. Addition of morepentane produced a second yellow crystalline product,identified as an isomer of o-metallated [Re(C0),L3(HL3)], Itwas recrystallised from pentane (Found: C, 62.0; H, 4.05; N,7.0. C41H31N4Re requires C, 60.5; H, 3.8; N, 6.9%). The massspectrum of the second isomer was identical to that of thefirst isomer which is discussed further below.1.r. (NujoI):v(N-H) 3 341m; v(C0) 2 016vs, 1 912vs, and 1 873vs cm-'.I-- II/Reactions of [Re(C0)4L] (L = L4, L', or L2) with Amidines(HL4, HL', and HL2 respectively).-The reaction conditionsand procedures were identical to those described above. Theproducts were the o-metallated complexes [ Re(CO),L(HL)],which are described in detail later.mReaction of [Re(CO),Br] with p-MeC,H,NHC( Me)N-C,H,Me-p.-(i) HLZ (1.72 g, 4.92 mmol) and [Re(CO)5Br](1.00 g, 2.46 mmol) were suspended in monoglyme (40 cm3)and the mixture refluxed for 3 h. After removal of the solventin vacua, the residue was extracted with toluene (10 cm3) andthe filtered solution cooled to - 10 "C. The crystalline product(1.26 g) consisted of two components, one yellow and theother white.Evaporation of the mother-liquor, then extractionof the gummy residue with carbon tetrachloride gave a paleyellow solution which on adding pentane and cooling yieldedsmall quantities of [Re(CO),(HL2)Br] and HL2.HBr.The mixture of yellow and white precipitates were heated incacuo; a faint sublimate of HLZ appeared on the cold-finger at145 "C. Further heating caused the mixture to melt at 190 "C,followed by the formation of a yellow deposit on the cold-finger. Recrystallisation of this material from toluene-pentane mixtures gave yellow crystals of o-metallated[Re(C0)3L2(HL2)]. An i.r. spectrum of the residue fromthe attempted sublimation showed only the yellow product tobe present. By comparison with the white product formedfrom an identical reaction using [Re(CO)sCI] as the reactant,the white product isolated in this reaction is believed to beData for o-metalfated [Re(C0)3L2(HL2)].In the mass[ Re(C0)3( H L2),Br]. mspectrum the parent ion ['87Re(CO)3b(HL2)]+ wasdetected at m/e 746. Subsequent fragmentation was by eitherloss of HL2 or carbonyl groups (see below); [Re2(CO),(L2),] +[ Z b 7 18 ___t 670 ___) 662-co -co - HL'I I t452 - .f[Re(CO),L'(HL')] + [ ReL2] +m/e 424 mle 746I- 508 __t 480- HL2 -co - co - cowas observed to higher m/e values than the product complex.The mass spectrum of the white product was identical to thatof o-metallated [Re(CO),L'(HL')]. 'H N.m.r. (CDC13) : 8 6.78(m), 2.28 (3), 2.17 (l), 2.08 (l), 1.68 p.p.m.(1).(ii) Using a large excess of HL2 over [Re(CO),Br] (8 : 1molar ratio), but an identical procedure to that describedmabove, the yellow product, o-metallated [Re(C0)3L2(HL2)],was isolated in 60% yield by fractional recrystallisation from amixture containing excess amidine and its hydrobromide salt.Reaction of [Re(CO),Br] with PhNHC(Me)NPh.-Theamidine HL' (1.372 g, 6.54 mmol) and [Re(CO)5Br] (0.885 g,2.18 mmol) were suspended in monoglyme (50 cm3) and themixture heated at the reflux temperature for 5.5 h. The palegreen solution was allowed to cool, the solvent removed invacuo, and the residue extracted with toluene (10 cm3).Pentane (2 cm3) was added to the filtered extract solutionwhich was then cooled to -10 "C.A pale yellow solidseparated, which after filtration from the mother-liquor, wasrecrystallised from toluene-pentane mixtures to yield paleyellow crystals of o-metallated [Re(CO)3L'(HL')] (yield0.85 g, 56%).Addition of more pentane to the mother-liquor and furthercooling produced more product, [Re(CO),(HL')Br] andHL'SHBr, which were separated by fractional crystallisationprocedures. In the mass spectrum of [Re(CO),k,'(HL')] theparent ion was detected at m/e 693 with daughter ionscorresponding to two fragmentation pathways (see below);-co -co -co H L'1- 662 634 ___). 606 -,[Re(CO),L'(HL')]+m/e 690[ ReL'] +m/e 3963. I- 480 ___)_ 452 __+ 424 --HL' -co - co -co[Re,(CO),(L*),]+ was detected to high mass values of theparent product ion.Metastable peaks were not observed. 'HN.m.r. (CDC13): 6 7.26 (m), 2.10 (l), 1.68 p.p.m. (1).Reaction of [Re(CO),Br] with PhNHC(Ph)NPh.-Using anidentical procedure to that described above with the reactants[Re(CO),Br] and HL3 in a 1 : 3 molar ratio, yellow crystalsof o-metallated [Re(C0),L3(HL3)] were obtained in 60%yield. In the mass spectrum the parent ion was observed atm/e 814 with daughter ions corresponding to two fragment-ation pathways (see below); [Rez(C0)6(L3)2] + was detected tohigh mass values of the parent ion.I-co ~ co -co -HL3 1- 786 758 ___+ 730 -n t514 __+ 486 - -f[ Re(C0)3L3( H L3)] + [ReL3]+mle 814 m/e 458-HL3 -co -co -co 1- 54J . CHEM. SOC. DALTON TRANS. 1983 2623Reaction of [Re(CO)5Br] with p-MeC6H4NHC(Ph)NC6H4-Me-p.-Using the reagents in a 1 : 3 molar ratio, the proceduredescribed above was adopted for the reaction though theproduct separation method used was different.At the end ofthe reaction after evaporation of the solvent, extraction of theresidue with toluene (10 cm3) and addition of pentane to thefiltered solution produced a gummy precipitate at -10 "C.The gum and the pale yellow solution above were thentreated separately.The solution was filtered through alumina (2-cm column),then evaporated in vucuo to small bulk before the addition ofpentane. The yellow product formed on cooling to -10 "Cwas shown by i.r. spectroscopy to be a predominantly o-metallated [Re(C0),L4(HL4)] with impurities of [Re(C0)4-(HL4)Br] and a second tricarbonyl complex, identified lateras [Re(C0),(HL4),Br].The mixture was heated in uacuo in anattempt to remove impurities by sublimation, but the mixture1 - 7melted at 180 "C and pure o-metallated [Re(C0),L4(HL4)] wascollected on the cold-finger, although at a slow rate at 190 "C.Recrystallisation of the residue from toluene-pentane mix-tures was preferred, and yellow crystals of o-metallated[Re(C0)3L4( HL')] were obtained (yield 0.51 5 g, 28%).The yellow gum was heated to 70 "C in vacuo for 2 h andcrisp yellow flakes of a new tricarbonyl complex were producedwith HL4-HBr. Recrystallisation twice from diethyl ether-pentane mixtures gave yellow crystals of a second isomerof o-metallated [Re(CO)3k4(HL4)] (yield 0.13 g, 7%). 'HN.m.r. (CDCI,): 6 (isomer I) 6.89 (m), 2.20 (3), 2.09 p.p.m.(1); 6 (isomer 11) 6.83 (m), 2.17 (3), 2.07 p.p.m.(1). The massspectra of the two isomers were identical, the parent ion beingobserved at mje 871. Daughter ions correspond to two frag-mentation pathways (see below); [Re2(CO),(L4),]+ was- co -- co -co -HL4 -+1- 571 ___t 543 __I+ 515 ~ .f1- 843 - 815 787 - [Re(CO),L4( H L4)] + [ ReL4] +mle 871 m/e 487-HL4 -co -co - codetected to high mass values of the parent ion. Metastablepeaks were not observed.Reaction of' [(Re(C0)4Br}2] with PhNHCHNPh.-A mixtureof the carbonyl (0.500 g, 0.661 mmol) and HL5 (0.777 g, 3.97mmol) in monoglyme (30 cm3) was heated at reflux for 1.5 h.The solvent was then removed in vacuo from the pale yellowsolution, and the residue extracted with toluene (10 cm3).Addition of pentane (4 cm3) and cooling to - 10 "C producedyellow crystals of o-metallated [Re(CO)3LS(HLs)] whichwere recrystallised from toluene-pentane (yield 0.421 g, 48%).In the mass spectrum the parent ion was observed at m/e 662with daughter ions corresponding to two fragmentationpathways (see below); [Re,(C0)6(L5)2]+ was detected to highmass values of the parent ion.- co -~ co -HL5 ++r& 634 - 606 ---+ 578I I[ Re(CO),L5(H L')] + [ ReL5]m/e 662 mle 382I- 466- 438 __t 410 --HL5 co - co -coReaction of [Re(CO),CI] with p-MeC6H4NHC( Me)N-C6H&k-p.-(i) 1 : 3 Molar ratio.The procedure adopted wasidentical to that described above for the bromide complex.Hexane extraction of the original residue of the reactiongave yellow crystals of o-metallated [Re(CO)3L'(HL')](yield 0.259 g, 25%).The remaining residue consisted of amixture of complexes, which were separated by fractionalcrystallisation from chloroform-hexane mixtures followed bysolvent extraction with light petroleum (b.p. 100-120 "C)at 80 "C. The hot extract yielded white [Re(C0)3(HL2)2CI](yield 0.416 g, 38%). 'H N.m.r. (CDC13): 6 7.09, 7.03 (8),6.02, 5.90 (l), 2.33 (6), 1.63 p.p.m. (3).The parent ion in the mass spectrum was observed as aweak peak at m/e 782. Thermal decomposition in thesourcecaused loss of HCl and the formation of the o-metallated[Re(C0)3LZ(HL2)], and the remaining spectrum wasidentical to that obtained for an authentic sample of thelatter complex.(ii) 1 : 2 Molar ratio.The reaction procedure was identicalto that described immediately above. The products, [Re(CO)3--1 - 7(HL2)tCI], o-metallated [Re(CO)3i'(HL2)], and [Re(CO)'-(HL2)Cl], were separated by fractional crystallisation methods.Reaction of [Re(CO),Br] with p-MeC6H4N(Me)C( Me)N-C6H4Me-p.-A mixture of [Re(CO),Br] (0.500 g, 1.23 mmol)and HLZm (0.931 g, 3.69 mmol) in monoglyme (40 cm3) washeated to the reflux temperature for 2.5 h, forming an orangesolution. On cooling a white precipitate of HL2"*HBr (0.212g) separated. Evaporation of the filtered solution in uucuogave a gummy residue which was extracted with toluene(10 cm3). Chromatography on an alumina column usingtoluene as eluant removed HLZm but left the product complexabsorbed on the alumina.Soxhlet extraction of the aluminawith monoglyme, followed by reduction in volume of thepale yellow solution and cooling to -10 "C yielded paleyellow crystals of o-metallated [Re(C0)3L2m(HL2m)] (yield0.113 g, 12%). The parent ion in the mass spectrum wasobserved at m/e 774. Fragmentation was complex with initialloss of CH2 or CO; principal daughter ions are indicatedbelow. No metastable peaks were observed.1 - 1- CH2 -HLZm ,- 760-1 - - 7[Re(C0)3L2m(HL2m)] +m/e 774I- 718 __t 702 _I+C-- 2co - CH4 -co- 3CO508 t+ [ReL2]+m/e 424674 ~ - H ~2~Reaction of o-Metaffated [Re(C03)L2m(HL2m)] withPPh3.-A mixture of PPh3 (0.035 g, 0.13 mmol) and the com-plex (0.100 g, 0.13 mmol) dissolved in toluene (10 cm3) wasstirred at room temperature for 24 h.Reduction of the volumeof the solution in vacuo and cooling to -10 "C produced awhite solid identified as [Re(C0)3(PPh3)L2] which has beendescribed earlier in this paper (yield 0.08 g, 80%).I - - IReactions of Other o-Metalfated [Re(CO),L(H L)] Com-plexes with PPh3.-The complexes [Re(C0)3(PPh3)L], whereL = L', L4, and L3, were similarly prepared by the proceduredescribed above.Reaction of o-Metaflated [Re(CO),L2(HL2) with HBr.-A small sample of the complex was suspended in methano2624 J. CHEM. SOC. DALTON TRANS. 1983(10 cm3) and hydrobromic acid (47% aqueous solution) wasadded dropwise. The solid changed colour from yellow towhite. The liquid was removed by syringe and the whiteresidue washed with methanol before drying in vucuo.1.r.spectroscopy provided identification of the product as [Re-(C0)3(HLZ)2Br] by comparison with an authentic sample.Reactions of [Re(C0)4(COL)] and [Re(C0)4L] Complexeswith Amidines.-The formation of o-metallated products bythese routes is described earlier and elsewhere.22AcknowledgementsWe thank the S.E.R.C. for a studentship (to J. A. C.).References1 L. Toniolo, A. Immirizi, V. Croatto, and G. Bombieri, Inorg.2 T. Inglis, M. Kilner, T. Reynoldson, and E. E. Robertson,3 T. Inglis and M. Kilner, J. Chem. SOC., Dalton Trans., 1975,4 M . Kilner and B. Gaylani, J. Less-Common Met., 1977, 54,5 N. D. Cameron, M. Kilner, M. Mahmoud, andS. C. Wallwork,6 E. W. Abel and S. J. Skittrall, J. Organomet. Chem., 1980, 193,7 W. H. de Roode, D. G. Prins, A. Oskam, and K. Vrieze, J.8 W. H. de Roode, J. Berke, A. Oskam, and K. Vrieze, J . Organo-9 W. H. de Roode, M. L. Beekes, A. Oskam, and K. Vrieze, J.10 F. A. Cotton, T. lnglis, M. Kilner, and T. R. Webb, Inorg. Chem.,1 1 M . G . B. Drew and J. D. Wilkins, Acta Crystallogr., Sect. B,Chim. Acta, 1976, 19, 209.J . Chem. Soc., Dalton Trans., 1975, 924.930.175.unpublished work.389.Organomet. Chem., 1978, 154, 273.met. Chem., 1978, 155, 307.Organomet. Chem., 1977, 142, 337.1975, 14, 2023.1975, 31, 2642 and refs. therein.12 W. Bradley and I. Wright, J. Chem. SOC., 1956, 641.13 L. Toniolo, T. Boschi, and G. Deganello, J. Organomet. Chem.,1975, 93, 405.14 W. H. de Roode and K. Vrieze, J. Organomet. Chem., 1978,145,207.15 F. A. Cotton, W. H. Isley, and W. Kaim, Znorg. Chem., 1980,19, 2360; F. A. Cotton and L. W. Shive, ibid., 1975, 14, 2027.16 L. Toniolo, G. Deganello, P. L. Sandrini, and G. Bombieri,Inorg. Chim. Acta, 1975, 15, 1 1 .17 P. I. van Vliet, G. van Koten, and K. Vrieze, J. Organomet.Chem., 1980, 188, 301.18 N. D. Cameron, R. J. Eales, and M. Kilner, Abstr. 7th h i .Conf. Organomet. Chem., Venice, 1975, 119; M. Kilner, un-published work.19 F. A. Cotton, W. H. Isley, and W. Kaim, Inorg. Chem., 1980,19, 2360.20 J. C. Halfpenny, unpublished work.21 A. F. M. J. van der Ploeg, G. van Koten, and K. Vrieze, Znorg.Chem., 1982, 21, 2026.22 J. A. Clark and M. Kilner, J. Chem. Soc., Dalton Trans., in thepress.23 N. D. Cameron and M. Kilner, J. Chem. SOC., Chem. Commun.,1975, 687.24 N. M. Boag and H. D. Kaesz, ‘ Comprehensive OrganometallicChemistry,’ eds. G. Wilkinson, F. G. A. Stone, and E. W.Abel, Pergamon, Oxford, 1982, vol. 4, p. 219.25 J. P. Collman and L. S. Hegedus, ‘ Principles and Applications ofOrganotransition Metal Chemistry,’ University Science Books,Mill Valley, California, 1980, pp. 213-228.26 G. W. Parshall, Acc. Chem. Res., 1970, 3, 139; P. M. Maitlis,P. Espinet, and M. J. H. Russell, ‘ Comprehensive Organometal-lic Chernistry,’eds. G. Wilkinson, F. G. A. Stone, and E. W.Abel, Pergamon, Oxford, 1982, vol. 6, p. 320.27 N. Ahmad, E. W. Ainscough, T. A. James, and S. D. Robinson,J. Chem. Soc., Dalton Trans., 1973, 1148.28 E. W. Abel, G. W. Hargreaves, and G. Wilkinson, J . Chem. SOC.,1958, 3149.29 J. D. Atwood and T. L. Brown, J. Am. Chem. SOC., 1976, 98,3 155.Received 28th March 1983; Paper 3149

ISSN:1477-9226    

DOI:10.1039/DT9830002613

出版商:RSC    

年代:1983

数据来源: RSC