摘要:
1975 2306 lsocyanide Complexes of Platinum(0) By Graham A. Larkin Ronald Mason and Malcolm G. H. Wallbridge,*#t Department of Chemistry, Treatment of [Pt(C,H,) (PPh,),] with t-butyl isocyanide yields the complex [Pt(CNBut),(PPh,),] and evidence for the existence of related species [Pt(CNR),(PPh,),] (R = Pr' C6Hll. p-MeOC,H, or p-CIC6H,) has been obtained from solution studies. Displacement of the arsine ligand from [Pt(AsPh,),(C,F,)] with RNC (R = Pr' or But) yields the complexes [Pt(CNR),(C,F,)]. Oxidative-addition reactions of [Pt(CNBut),(PPh,),] occur with I, Met CF,I and [SnPh,CI) the products being best formulated as [Pt(CNBut),(PPh3),I]I or [Pt(CNBut)(CR= NBut)(PPh,),]l except for the adduct with [SnPh,CI]. Alternative routes to some of the products have been found such as the interaction of [PtMe(l)(PPh,),] with ButNC.An unusual reaction occurs on attempted alkylation of the cyanide [Pt(CN),(PPh,),] with Me1 in that the phosphine ligands are displaced and [Pt(CNMe),l,] is obtained. University of Sheffield Sheffield S3 7HF ISOCYANIDE complexes of the Ni,Pd,Pt triad illustrate particularly well some of the remarkable features associa-ted with this ligand and have consequently received considerable attention in recent years1 The majority of complexes isolated contain the metal in the bivalent state although some interesting differences are observed. Thus for nickel very few derivatives of Nirr are known, in contrast to the numerous complexes of PdII and PtII, and attempts to prepare them have led to ill defined products.2 On the other hand while several derivatives of zerovalent nickel e.g.[Ni(CNPh),] and [Ni(CNMe),-(CO)J,4 have been reported only a few ill defined Pd complexes are known. Malatesta has described a series of complexes [Pcl(CNR)J (R = Ph p-MeC,H, or &MeOC,H,) which were obtained by reduction of [PdI,(CNR),] using alcoholic potassium hydroxide. They are insoluble in organic solvents and appear to be polymeric. This view was substantiated by a study of similar PdO complexes [Pd(CNC6H11),] and [Pd(CNPri)J, prepared by the addition of the isocyanide to cyclo-hexenyl(cyclopentadieny1) palladium.6 Other palladium derivatives such as [Pd(CNR)(PR',)J (R = p-MeOC,H,; R' = $-MeC,H, @-c1c6H,o or PhO) ,' [Pd(CNR),L] [R = But or Ph; L = C,(CN),,8*9 fumaronitrile maleic anhydride dimethyl maleate C2Ph,,9 or (CF,),C=C-(CN),1O] and [Pd(CNPh){C,(CN),)(MPh,)] (M = P or As) have also been formed from [Pd(CNR),].How-ever the only Pto complexes known are [Pt(CNC,Hll)-(PFJ] isolated in the course of a kinetic study,ll the recently reported trimer [Pt,(CNBut) J,12 and those which we have described in a preliminary comm~nication.~~ The purpose of this paper is to report more fully on these latter complexes and on some related studies. t Pvesent address Department of Molecular Sciences Univer-sity of Warwick. (a) 'Isocyanide Complexes of Metals,' eds. L. Malatesta and F. Bonati Wiley-Interscience London 1969 ; (b) ' Isonitrile Chemistry,' ed. I. Ugi Academic Press London 1971. P. M. Treichel Adv. Organometallic Chem. 1973 11 21.H. Behrens and K. Meyer 2. Natwtforsch. 1966 B21 489. W. Hieber 2. Naturforsch. 1950 B5 129. L. Malatesta J . Chem. SOC. 1955 3924. E. 0. Fischer and H. Werner Ber. 1962 95 703. L. Malatesta and M. Angoletta J . Chem. SOC. 1957 1186. T. Boschi P. Uguagliati and B. Crociani J . Urganometallic S. Otsuka T. Yoshida and Y . Tatsuno J . Amer. Chem. Soc., lo H. D. Empsall M. Green S. K. Shakshooki and F. G. A. Chem. 1971 30 283. 1971 93 6462. Stone J . Chem. SOC. ( A ) 1971 3472. An extensive chemistry of complexes which contain PtO has been developed and many mixed phosphine-ligand complexes are known.14 These are generally of the composition [Pt (PR,),L] where L may be a variety of unsaturated ligands such as alkenes alkynes oxygen , and compounds containing >GO and >C=S bonds.The carbonyl complexes [Pt (CO)(PR,)J and [Pt (CO),-(PR,),] have also been prepared as have the trinuclear and tetranuclear clusters [Pt (CO),( PR,) ,] and [P t4( CO),-(PR,),] (n = 3 or 4).15 Since isocyanide ligands are isoelectronic with carbon monoxide and resemble both this ligand and tertiary phosphines in their x-acceptor ability they should also be capable of stabilising Pto in suit able complexes. RESULTS AND DISCUSSION Because of their ease of preparation Complexes con-taining PtO e.g. [Pt(PPh,),] ,l6 [Pt(PPh,)A,l' and [Pt-(C2H4) (PPh,)J lS were chosen initially as starting materials in this study especially since early results had indicated that such complexes are extensively dissociated in benzene solution affording the two-co-ordinate species [Pt(PPh3)d.19y20 Thus benzene solu-tions of these three complexes were treated with alkyl and aryl isocyanides and the i.r.spectra of the resulting solutions were examined in the 2 200-2 000 cm-l region to seek evidence of co-ordination. It is established that the strong NEC stretching frequency which occurs at 2 200-2 100 cm-l in the free isocyanide shows a signifi-cant decrease when the group is co-ordinated to a transi-tion metal in a low oxidation state.21 The addition of various isocyanides (Table 1) to l1 R. D. Johnston F. Basolo and R. G. Pearson Inorg. Chem., l2 M. Green J. A. Howard J. L. Spencer and F. G. A. Stone, l3 G. A. Larkin R. Mason and M. G. H. It'allbridge Ckem. ' Zerovalent Compounds of Metals,' eds.I,. Malatests and S. J. Chatt and P. Chini J . Chem. SOC. ( A ) 1970 1538. l6 R. Ugo F. Cariati and G. La Monica Inorg. Synth. 1968, l7 R. Ugo F. Cariati and G. La Monica Inoytg. Synth. 1968 11, C. D. Cook and G. S. Jauhal J . Anzer. Chem. SOC. 1968 90, lS L. Malatesta and C. Cariello J . Chem. SOC. 1958 2323. 2o 1. P. Birk J. Halpern and A. L. Pickard J . Amer. Chem. 21 See ref. l ( b ) p. 215. 1971 10 247. J.C.S. Chem. Cornm. 1975 3. Comm. 1971 1054. Cenini Academic Press London 1974. 11 105. 107. 1464. SOC. -1968 90 4491 2306 J.C.S. Dalton solutions of [Pt(PPh,),] (ut = 3 or 4) in a molar ratio RNC [Pt(PPh,),J 2 2 1 resulted in only one absorp-tion in the above region and a sharp decrease in the isocyanide (NX,) stretching frequency of the order of 50-100 cm-l indicating that co-ordination of the iso-cyanide had occurred.The addition of a further quantity of isocyanide caused the appearance of a further N-C absorption at the value corresponding to the free isocyanide indicating the presence in solution of previous solution studies and indicating appreciable back donation of charge from the metal to the ligand. Benzene solutions of the complex slowly deposit pale yellow crystals of the carbonate [Pt(CO,) (PPh,),] on standing in air thus showing similar behaviour to [Pt(PPh,),] (ut = 3 or 4).,,9% The methyl isopropyl cyclohexyl and 9-chlorophenyl derivatives failed to displace ethylene under similar conditions even after extended reaction times (5-6 h) at 0 "C. TABLE 1 Behaviour of various isocyanides in benzene solutions of [Pt(PPh,),] [Pt(PPh,),] and [Pt(C2H4) (PPh,),] a Complex [IPt(PPh3)4l [Pt(PPhJ3I [Pt(C2H4) (PPh3) 21 Isoc y anide\ ButNC (2 130) c ( 2 030) c (2 030) c (2 030) a PriNC (2 140) c (2 070) c (2 070) n.c.C6Hl,NC (2 140) c (2 070) c (2 070) n.c. p-MeOC,H,NC ( 2 130) c (2 020) c (2 020) n.c. p-C1C6H4NC (2 130) c (2 080) c (2 080) n.c. p-MeC,H,NC P P * The E C stretching band (cm-l) in the free (or co-ordinated) ligand is given in parentheses. c = Co-ordination n.c. = no co-ordination and p = polymerisation. b Recorded from a Nujol mull. a species [Pt(CNR),(PPh,),]. An exception to this be-haviour was observed with 9-tolyl isocyanide when after addition of 2 mol no absorption in the 2 200-2 000 cm-l region could be detected.While the fate of the isocyanide in this reaction is uncertain the most likely possibility is that polymerisation of the isocyanide occurs although only a weak absorption was observed in the region characteristic of polyisocyanides (1 645-1 615 cm-l). The results for benzene solutions of [Pt(PPh,),] and [Pt(PPh,),] are summarised in Table 1. We were unable to isolate the species [Pt(CNR),(PPh,),] from the benzene solutions of [Pt (PPh,),] the difficulty being caused by the similar solution behaviour of the product, starting material and triphenylphosphine in a range of solvents. The behaviour of the ethylene complex [Pt(C,H,)-(PPh,)J with various isocyanides is in sharp contrast to that of the phosphine complexes. In benzene solution, displacement of the ethylene and subsequent co-ordin-ation of the isocyanide was observed only in the case of t-butyl isocyanide and with all the other isocyanides examined no decrease in the N-C stretching frequency was observed in the i.r.spectra. The reaction with ButNC was best performed in pentane solution at low tempera-ture [equation (l)]. Ethylene was evolved quantitatively [Pt(C2H4) (PPh,),] + 2ButNC - - 20 oc n-pentane [Pt(CNBut)2(PPh3)21& -t C2H4.T. (l) during the reaction and the product precipitated from solution as a pale yellow solid which decomposes slowly in the air but is stable under dry nitrogen. The solid is moderately soluble in benzene and toluene and slightly soluble in n-pentane. The N-C stretching frequency occurred at 2 030 cm-l a value in agreement with the * 1 atm = 101 325 Pa.22 C. J. Nyman C. E. Wymore andG. Wilkinson Chem. Comm., 1967 407. From recent studies on the nature of the species present in solutions of [Pt(PR,),] (n = 3 or 4) and [Pt(C,H,)-(PPh,)J it has been suggested that [Pt(PR,),] species dissociate only to [Pt(PR,),] and that [Pt(PR,),] and [Pt(C,H,) (PPh,)J are both undissociated in benzene solution,%,% and it is only when R is a bulky group (e.g. C,H,,) that [Pt(PR,)J is stabilised.26 The present results may be rationalised in the light of this evidence in that one molecule of isocyanide adds to the co-ordina-tively unsaturated species [Pt (PPh,)?] together with substitution of phosphine by isocyanide to yield [Pt-(CNR),(PPh,),]. This situation is closely paralleled in the reaction of carbon monoxide with the [Pt(PPh&] complexes where substitution cannot be effected beyond the [Pt(CO),(PPh,),] stage.,' In the case of [Pt(C,H,)-(PPh,),] the results imply that for the different isocyanides used the relative nucleophilicity of the ligand is important in that only ButNC will displace the ethylene.However, since the stability of complexes of the type [PtL(PPh,),] evidently depends on the delicate interaction of 0- and n-bonding effects any extension of the comparison to other ligands would be unwise. When solid [Pt(CNBut),(PPh,)J was treated with a modest (ca. 25 atm) * pressure of carbon monoxide 1 rnol of isocyanide was displaced and the carbonyl [Pt(CNBut) (CO)(PPh,),] was obtained as a pale yellow solid [equation (2)].In this complex the NEC stretching [Pt(CNBut),(PPh,)J --t mode occurred at 2 110 cm-l (with the C-0 mode at 1910 cm-I) and in comparison with the bis(isocyanide) (2030 cm-l) this higher value suggests that the CO ligand competes more effectively than ButNC for the overall charge on the metal atom. This conclusion is co [Pt(CNBut)(CO)(PPh,),] + ButNCt (2) 24 C. A. Tolman W. C. Seidel and D. H. Gerlach J . Amer. 25 H. C. Clark and K. Itoh Inorg. Chem. 1971 10 1707. 26 A. Immirzi and A. MUSCO J.C.S. Chem. Comm. 1974 400. 27 P. Chini and G. Longoni .I. Chenz. Soc. ( A ) 1970 1542. Chem. Soc. 1972 94 2669. 23 .F. Cariati R. Mason G. B. Robertson and R. Ugo Chem. Comm. 1967 408. - . 1975 2307 consistent with previous studies on mixed isocyanide-carbonyl compounds e.g.[Ni(CNR),(CO),] (n = 1-3), containing metal atoms in the zerovalent The lH n.m.r. spectra of both the carbonyl and bis-(isocyanide) complexes [Pt(CNBut)L(PPh3)d (L = But-NC or CO) in deuteriated benzene solution were simple, showing a sharp singlet for the But group(s) and a multiplet for the Ph protons. The i.r. n.m.r. and microanalytical data for these complexes are in Table 2. In view of the several reported examples of addition Compound ( Pt (CNBut ) (CO) I PPhJ [Pt(CNBut),I( PPh,),] I 1 Pt(CNBut),(Me) I (PPh,),] [ Pt(CNBut) dPPh3) 21 [Pt(CNBut),(CFJ I (PPhJ 13 [Pt(CNBut),(PPh,),][SnPh,CI] [Pt(CNBut),(C,F,)] i [Pt(CNPri),(C,F,)] b RutNC The fact that oxidative addition had occurred in every case was clearly established from a sharp rise in the N-C stretching frequency in the products to values in the range 2 225-2 190 cm-1 which is higher than that of the free isocyanide and typical of isocyanides bonded to PtII.The products obtained from I, MeI and CF31 exhibit appreciable conductivity in nitromethane (Table 2) all showing values typical of or closely approaching, a 1 1 electrolyte. However the product from [Sn-Ph3C1] shows a much lower conductivity suggesting only TABLE 2 Analytic spectral and conductivity data for the isocyanide complexes Analyses a/% 1.r. spectra (cm-I) b ' c 61 7 62 4) 60:3 I60:7) 48.1 (48.5) 54.9 (54.8) 51.2 (52.2) 60.4 (60.5) 31.7 (31.2) 27.7 (27.7) H N Halogen 5.3 (5.4) 3.1 (3.2) 4.3 (4.7) 2.0 (1.7) 4.3 (4.2) 2.7 (2.5) 21.4 (22.3) 5.0 (5.0) 2.4 (2.7) 12.8( 12.4) 4.7 (4.5) 2.6 (2.6) 11.3 (11.7) 4.9 (5.0) 1.2 A (2.2) 2.6 (2.8) 4.1 (3.9) 6.2 (6.1) 3.4 (3.2) 6.4 (6.5) '"(NC) Other absorptions ' 2 030 2 225 2 200 2 220 v(CF) 1040-1 010 2 190 2 110 v(C0) 1910 2 207 "(CF) 1100-1 030 2 185 2 230 v(CF) 1 100-1 030 2 212 2 130 m N.m.r.spectra * r T(Ph) c W) d 2 4 - 3 l(m) 30) 2:1-3:0(m) 130) 2.0-2.6(m) (30) 2.2-2.7(m) (30) 2.3-2.8(m) (30) 2.5-3.6(m) (45) 122.8 J 81.2 1 A (in 9.1(s) (18) e 9.3(s) (9) e 9.25(s) (18) f 87.2 8.7(s) (9) 64.4 8.7-9.4(m) 72.5 9.3(s) (9) f '81.Y9.4(,) 21.1 !.277:s) f 8.48,8.37 (CH,),Z 5.82(CH) 8.53(s) n a Calculated values are given in parentheses. b Recorded as Nujol mulls or KBr discs.e s = Singlet and m = multiplet; relative intensities are given in parentheses d Relative to trichlorofluoromethane increasing to high field. e In CEDI. I In CDCIJ. o The value in MeJO is 116 S cm* mol-l. Typical values for 1 1 salts in MeNOi and Me&O are 80-100 and 120-160 Scm* mo1-I respectively. A Persistently low analysis. 6 M.p. 133-135 "C (decomp.). f In CDCl,; Jptp 316 Hz. k M.p. 146-148OC (decomp.). In CH&I,; JPtF 408 Hz. fi) Liquid film. n In CHCI,. reactions to [Pt(PPh,)J (n = 2-4),14 we attempted similar reactions with the complex [Pt (CNBut),(PPh3),-J. Typically phosphine elimination occurred in the former case [equation (3) n = 0-2; RX = alkyl acyl aroyl, CPt(PPh,) - ,I + RX + [Pt(PPh3),(R)XI (2 - n)PPh3 (3) halogeno-olefin acetylene and metal halide].It is evi-dent from our studies that the presence of the isocyanide ligand modifies the course of the oxidative-addition re-action. The addition of 1 mol of reagents such as I, MeI, CF31 and [SnPh,Cl] to a benzene solution of [Pt(CNBut),-(PPh,),] at ambient temperatures yielded yellow solid products of empirical formula [Pt (CNBut),(PPh,),]*RX, although some noteworthy differences were observed in the type of product obtained. With iodine the product is quite stable and can be recrystallised from boiling benzene or dichloromethane-diethyl ether mixtures but the reaction products from the other reactions decompose slowly when left in solution and could not be recrystal-lised. However with these complexes it was possible to obtain pure complexes from the crude reaction product by rapid extraction with dichloromethane [equation (4)].[Pt(CNBut),(PPh,),] + RX - 'EHE 25 O C [ Pt ( CNBut ) (PPh,) ,R] X or [Pt (CNBut),(PPh3)J*RX (4) 28 F. A. Cotton and F. Zingales J . Amer. Chem. Soc. 1961 83, 29 RS. Bigorgne and A. Bouquet J . Organometallic Chem. 1963, 361. 1 101. partial dissociation or possibly that more rapid decom-position takes place. Products with similar empirical formulations to those reported above have been obtained from dihalogenoplatinum(11) complexes [Pt (PR3),X,], by reaction with MeNC in benzene solutionm or from [Pt (CNMe),(PR3)d[BF4] by reaction with [Me4N]I in dichl~romethane.~~ The products were suggested to contain five-co-ordinate PtII cations principally on the basis of conductivity data and an intense yellow colour-ation [e.g.equation (5) X = Br or I]. The variation in [Pt(PPh,),X,] + 2MeNC --t the type of product from this type of reaction is illus-trated by the fact that with the dichloride in benzene solution displacement of phosphine occurs and a four-co-ordinate species [Pt (CNMe)Cl,(PPh,)] results.m The most suitable description of the 1 1 adducts in the present work is that they may be of two types that is either [Pt (CNBut ),( PPh,),X] X or [Pt (CNBut) (C( X) = NBut )(PPh,),]X containing five or four-co-ordinate cations respectively. The general limited solubility and instability in solution of the oxidative-addition products prevented reliable molecular-weight data being obtained and although satisfactory conductivity data were recorded from nitromethane solution for the adduct with methyl iodide reasonable molecular weight and con-ductivity measurements were obtained using acetone solution.The lH n.m.r. spectrum of a freshly prepared 30 P. M. Treichel W. J. Knebel and R. W. Hess J . Amer. 31 P. M. Treichel and W. J. Knebel J . Co-ordination Chem., [Pt (CNMe) 2 (PPh3) 2x1 x (5) Chem. SOC. 1971 93 5424. 1972 2 67 2308 J.C.S. Dalton solution of [P~(CNBU~)~I,(PP~,)~ in deuteriochloroform showed a complex multiplet at T 2.0-2.6 attributable to the Ph protons and a singlet a t 7 9.25 arising from the protons of the But group with an overall integration ratio of 30 18. This togetherr with the other data indicates that this adduct is best!fonnulated as containing the five-co-ordinate cation * [Pt(CNBut),I(PPh,),!+.The spectra of the remaining adducts were less satisfactory in that although the integrated intensities of the two sets of signals were as expected (30 18) the signal from the But protons appeared as a pair of poorly resolved singlets a t z 8.7 and 9.3 for [Pt(CNBut)(Me)I(PPh,),] (no clear singlet signal from the Me group could be detected) , while for the CF,I and [SnPh,Cl] adducts the But protons appeared as poorly resolved complex multiplets. We therefore assume that in these cases decomposition occurs in the solution or that rearrangement of the cation occurs yielding a four-co-ordinate species as formulated above. However it is difficult to distinguish between the various possibilities a t present.The four-co-ordinate cations should possess inequivalent But groups which should be reflected in the n.m.r. spectra, but the complexity of the resonances suggest further reactions are occurring and we are unable to assign with certainty any absorption in the i.r. spectra arising from C=N vibrations although weak absorptions did occur in the 1600-1 500 cm-l region. Only for the iodine adduct can we propose with confidence the existence of a five-co-ordinate cat ion. Results from other workers support the view that rearrangement reactions are likely in five-co-ordinate coupling) and a C=N absorption of medium intensity a t 1 585 cm-l in the i.r. spectra. Of the complexes reported here it is [Pt(CNBut) (Me)I(PPh,),] which approaches this pattern most closely and appears therefore to con-t ain the [Pt ( CNBut ) ( CMe=NBut) (PPh,),] + cation.We prepared two of the above 1 1 adducts by an alternative procedure using PtII precursors. The reac-tion of BdNC with [Pt(PPh,),(X)Y] afforded products which had identical properties to the respective 1 1 adducts prepared as above e.g. equation (7). The re-[PtMe(I)(PPh,),] + 2ButNC + (7) actions of the isocyanide with [Pt(PPh,),(X)Y] (XU = CF31 or [SnPh,Cl]) were not studied since attempts to prepare the necessary precursors by oxidative addition of the halides to [Pt(PPh3),3 were unsuccessful. In each case tAhe dihalides [Pt(PPh,),XJ (X = C1 or I) were ob-tained the reaction with [SnPh3C1] being contrary under our conditions to that reported earlier.34 An inde-pendent attempt to prepare [PtCl(PPh,),(SnPh,)] from [Pt (PPh3)4] and [SnPh,Cl] also yielded the dichloride [PtC12(PPh3),] 35 although trimethyltin chloride has been reported to react with [Pt(PMePh,),] to yield trans-[PtCl(PMePh,),(SnMe,)] .z6 A summary of the main reactions is given in the Scheme.As an alternative route to the Me1 adduct we attempted to alkylate the cyanide complex [Pt (CN),(PPh,)J with methyl iodide. At the temperature required to effect the methylation (80-100 "C) an interesting side reaction occurred in that the phosphine was eliminated and the [ P t Me (CN But ) ( PP h,) 2] I ( i i l / v i l / \< 1 I ri!, [Pt (CNBu' I2 (PPh3)2] [ SnPh,CI] J [Pt (CNBu' )2(CF3)(PPh312] I SCHEME (i) 2 ButNC; (ii) C,H a t 25 "C; (iii) MeI; (iu) I,; (v) 25 atm CO; (vi) CF31; (viz) [SnPh3C1].cations containing a Pt-C b0nd.3~?3~ Thus insertion reactions of the type (6) ( X = Br or I) have been reported suggesting that the four-co-ordinate cation is favoured in [PtPh(PPh,),X] + MeNC --f [Pt(CPh=NMe) (PPh,),X] BleNC i [Pt(CNMe)(CPh=NMe)(PPh,),]X (6) these systems. In these cases the Me group in (C=NMe) showed a doublet in the lH n.m.r. spectra (from Pt-H 32 Y. Yamamoto and H. Yamazaki Co-ordination Chem. Rev., 1972 8 225. 33 P. M. Treichel K. P. Wagner and R. W. Hess Inovg. Chem., 973 12 1471. di-iodide [Pt(CNMe),I,] was obtained [equation (S)]. Similar alkylation reactions are well established for sealed [Pt(CN),(PPh,)J + MeI(excess) - tube [Pt(CNMe),I,] + ZPPh (8) several metal cyanides (Ag Cu etc.) but some unusual variations occur with platinum cyanide-isocyanide complexes since both alkylation and dealkylation reac-tions occur together with isocyanide in~ertion.3"3~>~~ 3* A.J. Layton R. S. Nyholm G. A. Preumatikas and M. L. 35 M. Fishwick and M. G. H. Wallbridge unpublished work. Tobe Chem. and Ind. 1967 464 1975 2309 Thus it has been reported that [Pt(CN)&] complexes (L = a phosphine ligand) cannot be alkylated with Me1 although no experimental conditions were given but with the more effective alkylating agent [R,O][BF,] (R = Me or Et) reaction proceeds easily in refluxing dichloromethane to yield [Pt(CNR),L,] [BF4]2.30 An attempt has been made to rationalise the influence of the difierent groups attached to the metal atom in these reactions and an explanation for the difference observed here may lie in the reaction conditions used since while it has been suggested 30 that the volatility and loss of Me1 may provide a driving force in the dealkylation reactions the reaction conditions in the present work iiivolve sealed tubes.I t is also noteworthy that at the reaction temperatures used no isomerisation of the isocyanide to the cyanide complex [Pt (NCMe),I,] occurred. We also made a limited investigation of the action of isocyanides on the complex [Pt (AsPh,),(C,F,)] prompted by the earlier observation that the arsine ligands are labile and may be replaced by a variety of pho~phines.~~ In contrast to these reactions where extended reaction times were required an instantaneous reaction occurred between the arsine complex and 2 mol of the isocyanide at ambient temperatures [equation (9) R = Pri or But].The products were obtained in g o d yields as air-stable white crystalline solids (Table 2) which decomposed slowly in chloroform solution over several days. A similar reaction using 9-chlorophenyl isocyanide afforded a reaction product which appeared to contain co-ordi-nated isocyanide (i.r. spectrum) but which was so insoluble that it could not be obtained in a pure state. Both the alkyl isocyanide products showed strong C-F absorptions (1 100-1 031 cm-l) in their i.r. spectrum (KBr disc) and a doublet in the NEC region (2 240-2 180 cm-l) (Table 2). This value is only 90-70 cm-l higher than that in the free ligand indicating that the isocyanide is accepting very little back donation from the metal.The two NEC vibrations suggest a square-planar arrangement around the platinum with the isocyanides in cis positions in spite of the difficulties associated with assignments from spectra of this type obtained from solid samples.,' The lH and I9F n.m.r. spectra (Table 2) were consistent with the above formulation. Thus the former showed reson-ances expected for the alkyl group of the isocyanide, while the latter showed one sharp line with satellites of relative intensities 0.25 from coupling with the 195Pt ( I = 5 relative abundance 34%) nucleus. The l9F n.m.r. spectra show a close similarity to those from [Pt(bipy)(C,FJ] and [Pt(AsPh,)(C,F,)] (bipy = 2,2'-bipyridyl). The values of Jptp observed for the isocyanide complexes were in the order predicted from 36 R.D. W. Kernmitt and R. D. Moore J . Chem. SOC. ( A ) 1971, 37 R. A. Walton Spectrochim. Acta 1965 21 1795. 38 J. Casanova N. D. Werner and R. W. Schuster J . Org. 2472. Ckeur. 1966 31 3473. the NEC stretching frequencies in the i.r. spectra and are consistent with previous results for the series [Pt(C,F,)L,](L = PPh, AsPh, bipy et~.).,~ It was observed for these complexes that high values of J P t ~ indicated a significant contribution from an ionic formulation [PtL,] [C,F,] and a similar conclusion appears to be valid for the isocyanide complexes. EXPERIMENTAL All solvents were dried (using lithium tetrahydro-aluminate calcium hydride or molecular sieves) and dis-tilled prior to use.1H N.m.r. spectra were recorded using Perkin-Elmer K12 (60 MHz) or Varian HA100 (100 MHz) spectrometers i.r. spectra on a Perkin-Elmer 457 Infracord. Our own experience of the preparation of isocyanides by the dehydration of N-monosubstituted formamides (see ref. 1 for summary) has been that while the use of dehydrat-ing agents such as phosphoryl chloride or toluene-p-sulphonyl chloride gave good yields of the alkyl isocyanides, only the POCl method gave appreciable yields of the aryl isocyanides. N-Methylformamide was purchased from B.D.H. Ltd. and N - t - b ~ t y l - ~ ~ N-isopr~pyl-,~~ and N-cyclohexyl-formamide39 were prepared by literature methods. The N-substituted aromatic formamides were prepared by the reported methods.40 The complexes, [Pt(PPh,),] l6 [Pt(PPh,),],17 [Pt(C,H,) (PPh,),],18 [Pt(Me) (1)-(PPh,) 2] ,41 [Pt (AsPh,),] ,3* [Pt (AsPh,) 2(C,F,)],36 and [Pt-(CN),( PPh,),] 42 were all prepared using published pro-cedures.Bis(b-butyl isosyanide)bis(triphenylphosphine)platinum-( 0 ) [Pt(CNBut),(PPh,)J.-To a stirred suspension of [Pt-(C2H4) (PPh,) ,] ( 1 . 0 g 1.34 mmol) in dry n-pentane (35 cm3) at 233 K under dry nitrogen t-butyl isocyanide (0.44 g, 5.36 mmol) was added as a solution in n-pentane (10 cm3). The reaction mixture was allowed to warm slowly to 253 K when an intense yellow colour developed. After 10 min at 253 K the mixture was stirred for a further 30 min a t 243 K. The mixture was then cooled further to 193 I<, transferred to a nitrogen-filled glove-box and filtered as quickly as possible.After washing with chilled n-pentane (10 cm3) the product was obtained as a yellow solid (yield ca. 80%) which was dried in vacuo. Reactions of [Pt(CNBut),(PPh,),] .-(a) With iodine. Iodine (0.143 g 0.565 mmol) was dissolved in dry benzene (10 cm3) and added dropwise to a stirred solution of [Pt(CNBut),(PPh3),] (0.5 g 0.565 mmol) in benzene (30 cm3) under nitrogen a t ambient temperature. The iodine colour was discharged and the yellow solid which pre-cipitated was filtered off washed successively with benzene (30 cm3) and hexane (30 cm3) and dried in vacuo. Yields of the principal product were ca. 60%. The complex was too insoluble in acetone for reliable molecular-weight measure-ments to be made. Methyl iodide (0.08 g 0.565 mmol) dissolved in benzene (10 cm3) was added dropwise to a solution of [Pt(CNBut),(PPh3),] (0.5 g 0.565 mmol) in benzene (30 cm3) under nitrogen at room temperature.The colour of the solution faded and became clear yellow on standing. After removal of all the solvent in vacuo the 39 I. Ugi R. Myer 39. Lipinski F. Bodesheim and F. Rosen-dahl Org. Synth. 1961 41 13. 4O I. Ugi and R. Myer Org. Synth. 1961 41 101. 4 1 J. Chatt and B. L. Shaw J . Chem. SOC. 1959 705. 4% J . C. Bailar and H. Itatani J . Arne?. Chem. SOC. 1967 89, (b) Wzth methyl iodide. 1592 2310 J.C.S. Dalton resulting oily yellow solid was washed with hexane. The pure solid was then extracted from this crude product with dichloromethane (ca. 10 cm3) the solvent quickly removed, and the resulting pale yellow solid finally stirred overnight under hexane.After filtration and washing with pentane, the solid (yield ca. 50%) was dried in vacuo M (cryoscopy, in acetone) GO7 (calc. for dissociated complex 514). (c) With triphenyltin chloride. The procedure adopted was identical to that given in (b) the same quantity of [Pt (CNBut),(PPh,) ,] being used and treated with [SnPh,Cl] (0.127 g 0.565 mmol). The product was obtained as a pale yellow solid (yield ca. 60%). The complex was too in-soluble in acetone for reliable molecular weight measure-ments. A slow stream of CF,I was passed into a benzene solution of [Pt(CNBut),(PPh,),] (0.5 g 0.565 mmol) under nitrogen a t room temperature until a clear pale yellow solution was obtained (after ca.5 rnin) . The benzene solution of the product was then worked up in the same way as the products from (b) and (c) the final yield being ca. 60%. Reaction of Di-iodobis(triphenylphosphine)pZatinum(II) with ButNC.-The isocyanide (0.1 g 1.03 mmol) in benzene (5 cm3) was added to a stirred suspension of [PtI,(PPh,),] (0.5 g 0.515 mmol) in benzene (30 cm3) and after stirring the reaction mixture for 15 min the intense yellow colour of the original solution had faded slightly. The solution was concentrated and the resulting yellow solid filtered off, washed with benzene and pentane and dried in vacuo. The product was identical with that obtained in (a) namely [Pt(CNBut)I(PPh,),]I and a near quantitative yield (0.51 g) was obtained (Found C 47.9; H 4.2; I 21.4; N 2.1.Calc. for C,,H,,I,N,P,Pt C 48.5; H 4.2; I 22.3; N, 2.5%). Reaction of Iodo(nzethyZ) bis(triphenylphosphine)platinum( 11) with ButNC.-Using similar reaction conditions to the above reaction with the di-iodide ButNC (0.089 g 0.107 mmol) was added to [Pt(Me)(I)(PPh,),] and the product (ca. 65% yield) was identical to the addition product obtained from the earlier reaction of [Pt(CNBut),(PPh3),] with Me1 (Found C 53.5; H 5.1; I 13.4; N 2.5. Calc. for C,,H,,IN,P,Pt C 54.8; H 5.0; I 12.4; N 2.7%). Preparation of CarbonyZ(t-butyl isocyanide) bis(triphenyZ-phosphine)platinum(O) [Pt(CO) (CNBut) (PPh,),] .-Solid [Pt-(CNBut),(PPh,),] (0.5 g 0.565 mmol) was treated with (d) With trifluoromethyl iodide. carbon monoxide a t 25 atm for 48 h and after this time a compacted yellow solid was obtained.The solid was stirred in hexane under nitrogen for 2 h when the product was obtained as a pale yellow powder; after removal of the solvent i t was dried by pumping in vacuo (yield ca. 80%) (Found C 60.3; H 4.3; N 2.0. Calc. €or C4,H,,NOP,Pt: C 60.7; H 4.7; N 1.7%). Reaction of Tris(triphenyZphosphine)platinum( 0 ) with TriphenyZtin Chloride.-The complex [Pt(PPh,),] (2.5 g, 2.55 mmol) and [SnPh,Cl] (0.98 g 2.55 mmol) were shaken together in benzene for 1 h. The white precipitate which was obtained was filtered off washed with both benzene and pentane and then dried in vacuo (Found C 55.2; H 4.4; C1,8.9. Calc. for C,,H,,Cl,P,Pt C 54.5 ; H 3.8; C1,8.9y0). Reaction of Dicyanobis(triphenylphosphine)platinum(n) with Me1.-The complex [Pt(CN),(PPh,),] (1.0 g 1.3 mmol) was heated in a sealed tube with excess of Me1 a t 373 K for 2 h.The resulting yellow precipitate was filtered off, washed with hexane recrystallised from dichloromethane, and dried in vacuo to yield yellow crystals. The i.r. spect-rum of the product showed a v(NC) absorption a t 2 230 cm-l, but no absorptions from Ph hydrogen atoms (Found C, 9.5; H 1.2; I 47.8; N 5.1. Calc. for CpH,I,N,Pt: C 9.0; H 1.1; I 48.0; N 5.3%). Reaction between But NC (and Pr'NC) and Tetrapuoro-ethyZenebis(triphenyZarsine)platinum( 0) .-A stirred suspen-sion of [Pt(AsPh,),(C,F,)] (0.9 g 1 mmol) in diethyl ether a t room temperature was treated with ButNC (0.16 g 2 mmol) dissolved in a small quantity of ether. A clear solution formed immediately and after stirring for 1 h the solvent was removed in vacuo. The crude solid was dis-solved in dichloromethane and reprecipitated with hexane. The colourless crystals [m.p. 134 "C (decomp.)] were washed with hexane and dried in uacuo average yield 60%. The preparation of the PriNC complex was achieved in a similar way except the colourless crystals [m.p. 147 "C (decomp.)] were precipitated on addition of absolute alcohol and yields averaged 55%. We thank the S.R.C. for the award of a maintenance grant, Mr. P. Tyson for help in recording the n.m.r. spectra and Mr. G. A. Wright for technical assistance during the preparation of the isocyanides. [4/1769 Received 21st August 1974
ISSN:1477-9226
DOI:10.1039/DT9750002305
出版商:RSC
年代:1975
数据来源: RSC