J. A m . Chem. SOC.1982, 104, 3891-3897 bath.,, They observed that the CD spectrum of [Co(sen)13+and its change with phosphate ions is similar to the A-[Co(en),]" case. HOWever, there was no interionic CT transition in the former system, unlike in the latter. Thus, it appears that the CT transition is not essential to the production of CD changes. We can find several other systems which show substantial CD changes due to additives but show no CT transition. These include A- [Co(en),] 3+.d-tartrate2-or ~ulfate.~'*~' Conclusion The finding that the association constants are different from One CD band to another has led us to postulate that detailed stereochemical information about ion pairs can be extracted from DCD studies. Though any detailed electronic mechanism leading to rotational strength changes could not be presented, we believe that the present finding should give an impetus to further works.
3891
Our own works aimed at the experimental demonstration of the validity of our postulate are in progress.
Acknowledgment is made to the Ministry of Education, Science and Culture (japan) for the donation of ~ ~ ~ ~ (~N ~ . B547043 and N ~ 434029). . Registry No. cis-[Co(en),(N,),]ClO,, 14877-87-3; cis-[Co(en),(N3)21I, 79270-30-7; cis-[Co(en)2(N3)~1Br, 15275-20-4; cis-[Co(en)z(N3)2]Cl,68265-39-4; ~is-[Co(en)~(Cl)~]CIO~, 23791-80-2; cis-[Co(en)z(Cl)2]Br,79270-31-8; cis-[C~(en),(CN)~]ClO~, 21861-61-0; cis[ c ~ ( ~ ~ ) , ( N o , ) , ] c ~1478 ~ , , 1-32-9;cis-[Co(en),(NCS),]+, 21 169-85-7; ,~-cjs-[Co(en),(CN),]+,18660-79-2; A-cjs-[C~(en),(NO~)~]+, 18660, A-cjs-[Co(en),(N,),]+, 78-1; l i - c i s - [ C o ( e n ) , ( N C S ) 2 ] +50762-67-9; 56906-68-4; A-~is-[Co(en)~(CI),]+, 18660-62-3;CI-, 16887-00-6.
(Trimethylphosphine)cobalt(I) Complexes. 1. Reactivity with Ethylene and Crystal Structure of
[CO(M~CN)(C~H~)(PM~~)~]BP~~.M~CN Brigitte C a p e l l e , l a Andre L. B e a u c h a m p , * l b Michele Yves Dartiguenave,*Iaand Hans-Friedrich Klein1'
Dartiguenave,*'"
Contribution from the Laboratoire de Chimie de Coordination du C N R S , AssociP d 1'UniuersitP Paul Sabatier, 31400 Toulouse, France, the DPpartement de Chimie, UniversitP de Montrdal C.P. 6210, MontrPal, QuZbec, Canada, H3C 3V1, and the Anorganisch-chemisches Institut der Technischen Uniuersitat, Miinchen, 0-8046 Garching. Germany. Received June 3, 1981
Abstract: The reaction of Co'Br(PMe,), with ethylene in various solvents was investigated at -80 and 35 OC by 31P('HJNMR spectroscopy. In toluene, acetone, and methanol, ethylene adds reversibly to the paramagnetic tetrahedral d8 Co' complex to give the diamagnetic CoBr(C2H,)(PMe3), species with C2H4 and Br in equatorial positions. Adding acetonitrile ( ] : I ) to acetone or methanol leads to a mixture of two pentacoordinate diamagnetic compounds: [Co(L)(C2H4)(PMe3),]Br (where L = C2H4 or MeCN) and [Co(MeCN)(C2H4)(PMe3),]Br. In the former, L cannot be unambiguously identified, but both L and C2H4have to be equatorial. In the latter species, the ligand distribution is the same as found in the crystals of the corresponding BPh4- salt, Le., C2H4 equatorial and MeCN axial. The same spectrum was obtained with [Co(MeCN)(C2H4)(PMe3),]BPh4.MeCN, which confirms that Br has been expelled from the coordination sphere of cobalt. The affinity of MeCN for Co' in this system is evidenced by the formation of the trigonal-bipyramidal (TBP) adducts [Co(MeCN)2(PMe3)3]+and [Co(MeCN)(PMe,),]+ in acetonitrile solutions of CoBr(PMe,), and [ C O ( P M ~ , ) ~ ] B Prespectively, ~,, at -80 OC. The reaction of ethylene with [Co(PMe3),]BPh, yields a TBP adduct [Co(C2H4)(PMe3),]BPh4with equatorial C2H4. The crystals of [CO(M~CN)(C,H,)(PM~,)~]BP~,, MeCN belong to space group P2,/c with a = 12.738 A, b = 28.52 A, c = 11.891 A, and p = 106.85'. The structure contains a distorted TBP [CO(M~CN)(C,H.,)(PM~,)~]+ cation in which MeCN and PMe3 are axial, whereas C2H4 and two PMe, ligands are equatorial. The ethylene double bond lies on the equatorial plane, and it undergoes the usual structural changes upon coordination. The distortions in the TBP are related to the individual steric requirements of each type of ligand.
The d8 RhC1(PPh3), complex is well-known for its ability to react with ethylene, giving rise to monomeric and dimeric molecular or cationic ethylene complexes. Its catalytic properties toward olefin isomerization and hydrogenation have been well investigated.2 The corresponding cobalt(1) compound CoC1(PPh3), is less r e a ~ t i v ealthough ,~ recently, ethylene dimerization has been reported to be catalyzed by CoBr(PPh,), in presence of BF3 as cocataly~t.~ The type of phosphorus ligand has an influence, since CoX(PR,), complexes with P(OEt)3, P(OPh),, and P(OMe), have
shown catalytic properties in the hydrogenation and isomerization of 01efins.~ However, up to now, few cobalt(I)-ethylene complexes with monodentate phosphorus ligands have been isolated. The synthesis of the first examples CoR(C,H,)(PMe,), (where R = Me, Ph, H), and [Co(C2H4)(P(OMe3),),]+ has been carried out recently by Klein et aL6>'and by Muetterties and Watson,8 respectively. The alkyl and aryl complexes have been synthesized by adding methyl or phenyl lithium to a tetrahydrofuran solution of C O C I ( P M ~ ,under ) ~ 1 atm of ethylene at low temperature. The formation of an ethylene adduct of CoC1(PMe3), as an inter-
( 1 ) (a) Laboratoire de Chimie de Coordination du CNRS. (b) UniversitB de Montreal. (c) Technische Universitat Miinchen. (2) (a) Osborn, J. A.; Jardine, F. H.; Young, J. F.; Wilkinson, G. J . Chem. Sot. A 1966, 171 1-1732. Herberhold, M. "Metal r-complexes"; Elsevier: Amsterdam, 1972; Vol. 11. Meakin, P.; Jesson, J. P.; Tolman, C. A. J . Am. Chem. SOC.1972, 94, 3240-3242. Tolman, C. A,; Meakin, P. 2.; Lindner, D.L.; Jesson, J. P. Ibid. 1974, 96, 2762-2774. Halpern, J.; Wong, C. S. J . Chem. SOC.,Chem. Commun. 1973, 629-630. (b) Schrock, R. R.; Osborn, J . A . J . Am. Chem. Soc. 1976, 98, 2134-2143, 2143-2147, 4450-4455. ( 3 ) Aresta, M.; Rossi, M.; Sacco, A. Inorg. Chim. Acta 1969, 3, 227-231. (4) Kawakami, K.; Mizoroki, T.; Ozaki, A. Bull. Chem. Sot. Jpn 1978, 5 1 , 21-24.
(5) (a) Vol'pin, M. E.; Kolomnikov, I. S. Dokl. Akad. Nauk SSSR 1966, 170, 1321-1324. (b) Gosser, L. W.; Parshall, G.W. Inorg. Chem. 1974, 13. 1947-1950. Gosser, L. W. Ibid. 1975, 14, 1453-1456; 1977, 16, 427-429, 430-434. (c) Rakowski, M. C.; Muetterties, E. L. J . Am. Chem. Sot. 1977, 99, 739-743. (6) Klein, H. F.; Hammer, R.; Wenninger, J., Gross, J. 'Catalysis in Chemistry and Biochemistry"; Pullman, B., Ed.; D. Reidel Publishing Co.: Amsterdam, 1979; p 285. (7) Klein, H. F.; Hammer, R.; Gross, J.; Schubert, U. Angew. Chem., Int. Ed. Engl. 1980, 18, 809-810. ( 8 ) Muetterties, E. L.; Watson, P. L. J . Am. Chem. SOC.1976, 98, 46654667; 1978, 100, 6978-6989.
0002-7863/82/1504-3891$01.25/0
0 1982 American Chemical Society
i
~
-
3892 J . Am. Chem. Soc., Vol. 104, No. 14, 1982
Capelle et al.
mediate, according to eq 1, has been suggested to explain the color change of the solution from blue to red, but the species was not characterized.
Crystal Data: Formula C39H5,BCoNZP3;fw 7 16.57; monoclinic, space group P2,/c, u = = 12.738 (4) A, b = 28.52 (1) A, c = 11.891 (4) A, P = 106.85 (3)O, V = 4134.5 A', d-1, = 1.151 g Z = 4, p(Mo Ka) = 5.5 cm-I, T = 23 O C , X(Mo K a ) = 0.71069 A (graphite monochromator). CoCI(PMe3)3 + C2H4 [CoC1(C2H4)(PMe3)31 X-ray Data Collection. Crystals for structure determination were Co(CH3)(C2H4)(PMe3)3 (1) obtained from the reaction mixture. They are orange-brown plates, along the c direction. They may be handled in air for the short We report here the reactions of ethylene on C O B ~ ( P Mand ~ ~ ) ~ elongated time needed to seal them in a Lindemann capillary filled with nitrogen. C O I ( P M ~in~ different )~ solvents. At room temperature, no deThe specimen used for data collection was cut from a longer plate, and tectable reaction occurs. However, lowering the temperature leads the dimensions of the fragment were as follows: 0.1 1 mm between faces to the formation of new diamagnetic species which are charac(100) and (TOO), 0.26 mm between (010) and (OTO), and 0.58 mm along terized in solution by 31PNMR. Solvent effect is important, since c. The fragment was not bounded by natural faces in the latter direction. The space group P2,/c was unambiguously determined from a set of the use of a polar and coordinating solvent, such as acetonitrile, precession photographs. The final unit-cell parameters were obtained by allows the isolation at low temperature of the ethylene cobalt(1) least-squares refinement of the setting angles of 25 reflections centered The crystal complex [CO(M~CN)(C~H,)(PM~~)~]BP~~-M~CN. in the counter aperture of an Enraf-Nonius CAD4 diffractometer. structure of this compound was examined for two reasons. First, The intensity data were collected by using the w/28 scan technique. the only known it is, together with [CO(C,H,)(C,H,)(PM~,)~], A fixed slit of 3.0 mm was used and the scan range was w = (0.90 to 0.35 X-ray structure of a cobalt(1)-ethylene complex and, although tan 8)' extended 25% on each side for backgrounds. Preliminary intheoretical models have been proposed, there is a lack of expertensity I was obtained from a prescan a t 6.7O min-I. All reflections imental information on the mode of bonding of ethylene with having I / a ( l ) < 1.0 were labeled "weak" and were not remeasured at first-row metal compounds in d8 electronic state. The second lower speed. For the final scan, a rate S between 6.7 and 0.7' min-' was automatically selected to make the I / a ( l ) ratio = 100, but a maximum reason is to determine the details of the stereochemistry, since scan time of 120 s was imposed. Three standard reflections were measuch complexes may play an important role as intermediates in sured every hour. Their intensities decreased regularly by 20% as a result chemical processes such as olefin dimerization, isomerization, of crystal instability. The decay was taken into account to scale the data hydrogenation, and so on. Since cationic species may present a a t the data reduction stage. Crystal orientation was checked every 100 different reactivity toward ethylene,2bwe also investigated the measurements. The actual position of the scattering vectors and the reactivity of [Co(PMe,),]+ with ethylene. directions derived from the orientation matrix always differed by 40°. The data H,PO, 62.5% was used as reference, and no temperature correction was were finally corrected for the Lorentz and polarization effects. Abapplied. A11 samples were prepared in the glovebox using dry deoxysorption correction was deemed unnecessary because o f the low absorpgenated solvents ((CD,),CO and/or CD,CN) and saturated with tion coefficient. ethylene at room temperature and 1 atm. Solution ' H N M R spectra Structure Determination and Refinement. The structure was solved by were measured with the same spectrometer, at variable temperature. the heavy-atom method and refined by full-matrix least squares. The Co They were referenced to tetramethylsilane. and one of the P atoms were located from a three-dimensional Patterson I R spectra were recorded on a Perkin-Elmer 137 spectrophotometer synthesis. A series of structure factor calculations and difference Fourier as Nujol mulls between KBr disks, using polystyrene as reference. (AF) syntheses revealed the positions of all the remaining nonhydrogen Magnetic susceptibility determinations in the solid state were done by atoms. Isotropic refinement converged to R = CllFol - IFcll/XIFol = the Faraday method using a Cahn microbalance coupled with a Drusch 0.079 (unit weights, observed reflections only). The 20 H atoms of the electromagnet. The experimental values are averages over three deterphenyl rings were then fixed a t their calculated positions with temperaminations a t 295 K. They are corrected for the diamagnetism of the ture factors U = 7.0 A'. The nonhydrogen atoms were anisotropically ligands9 refined, whereas the H atoms were fixed. This reduced the R factor to Microanalyses were performed by the Centre National de la Re0.048. In the subsequent AF map, most of the highest peaks (0.4-0.6 cherche Scientifique, Centre de Microanalyse, Lyon, France. e/A3) corresponded to H atoms on the methyl group of acetonitrile or Synthesis of the Complexes. PMe, was prepared following the method trimethylphosphine molecules. They were isotropically refined. They of Wolfsberger and Schmidbaurlo and stored under argon. CoBr(PMe3), reached reasonable positions which were used to define the orientation and CoI(PMe,), were synthesized following Klein and Karsch." They of the methyl groups. Torsion angles ~(c0-P-c-H) were calculated are very air sensitive. We were unable to get CoCI(PMe3), free of from these positions, and the three methyl hydrogens were fixed a t T , T OPMe,, and reactions with ethylene were not studied. 120, and T - 120' with C-H = 0.95 A and ideal tetrahedral angles. [CO(M~CN)(C~H~)(PM~~)~]BP~-M~CN. A solution of CoBr(PMe,), An average orientation was used when two hydrogens on the same methyl (1 g, 2.72 mmol) in acetonitrile (10 mL) is cooled to -10 O C and purged group had been refined in the first place. These hydrogens were assigned with ethylene. WaBPh, (0.93 g, 2.72 mmol), dissolved in a 1:l methatemperature factors U = 7.6 A'. Subsequently, the parameters of the nol-dimethyl ether mixture, is added. The solution cooled a t -80 OC methyl and phenyl hydrogens were not refined, but their coordinates were turns brown. The precipitated orange-brown crystal are filtered and dried recalculated after each least-squares cycle. under ethylene at -80 "C. Block-diagonal least squares were used for the rest of the refinement. Anal. Calcd for C3,H,,BCoN2P3: Co, 8.22; P, 12.97; N , 3.90; C, Anisotropic refinement at this stage converged to R = 0.040. In the new 65.37; H, 8.01. Found: Co, 8.12; P, 13.27; N, 3.26; C, 64.88; H, 7.83. AF map, the four hydrogens of the ethylene molecule showed among the six highest peaks (0.4-0.5 e/A'). They were introduced into the structure and were isotropically refined, simultaneously with the nonhydrogen ( 9 ) Foex, G . F. "Constantes Silectionnees-Diamagnitisme et atoms. No hydrogens could be found for the lattice acetonitrile molecule. Paramagnitisme"; Masson: Paris, 1957. In the latest stage of the refinement, individual weights are applied. ( I O ) Wolfsberger, W.; Schmidbaur, H. Synth. fnorg. Mef.-Org. Chem. The final R factor was 0.038 and the weighted residual R , = C[w(lFol 1974, 4, 149-156. - I F c 1 ) 2 / ~ w l F o 1 2= ] 10.042. ~2 The goodness-of-fit ratio was 1.08. In the (11) Klein, H. F.; Karsch, H. H. fnorg. Chem. 1975, 14, 473-477.
-.
+
J . Am. Chem. SOC.,Vol. 104, No. 14, 1982 3893
(Trimethy1phosphine)cobalt(I) Complexes
Table I. Refined Atomic Coordinates (X10'; X I O s for Co; l o 3 for H)
atom
6 (ppm) +20 +IO 0 -10 Figure 1. "P{'H) NMR spectrum of 0.1 M C O B ~ ( P Min~(CD3)~C0 ~)~ under an ethylene atomsphere ( T = -80 "C).
final AF map, the six strongest peaks (0.3C-0.18 e/A3) were within 1.0 8, of Co or P. The deepest valley was -0.22 e/A3. The scattering curves were those of Cromer and Waber except for hydrogen. Anomalous scattering was taken into account for Co and P.'* The refined coordinates are listed in Table I. The refined temperature factors and the coordinates of the fixed hydrogen atoms are part of the supplementary material.
Results Solution Study. Figure 1 shows the -80 OC 31P(1H)N M R spectrum obtained when an ethylene atmosphere is introduced into an N M R tube containing a 0.1 M solution of CoBr(PMe,), in deuterated acetone. The spectrum indicates the presence of a diamagnetic stereorigid species, characterized by a near firstorder AB2 pattern, in good agreement with the expected pentacoordinate adduct C O B ~ ( C ~ H ~ ) ( P(reaction M ~ , ) ~ 2). Increasing CoBr(PMe,), C2H4 CoBr(C2H4)(PMe3), (2)
+
the temperature causes a broadening of the spectrum, mainly due to complex dissociation, as evidenced from the temperature reversible color change of the solution from brown to -80 OC to violet at room temperature. An analogous spectrum is observed in methanol and in toluene (Table 11). The IH NMR spectrum (-80 "C) in deuterated actone shows broad lines for free ethylene at 6 5.4, for coordinated ethylene at 2.1 ppm8 and for the methyl protons of PMe3 at 1.5 and 0.7 ppm, respectively. Raising the temperature produces minor modifications of the PMe3 proton lines. The 31Pchemical shifts (Table 11) indicate that the geometry of the CoBr(C2H,)(PMe,), complex is most probably a distorted trigonal bipyramid with two axial and one equatorial PMe, ligands, corresponding to the low-field doublet ( 2 Pa) and the high-field triplet (1 Pe), respectively. Po
P,-0'
1
/'ZH4
I
B 'r
Deshielding is more important for the axial than for the equatorial PMe, ligands, in agreement with theoretical consideration^.'^ Similar observations have been reported for the analogous NiX2(PMe,), d8 c0mp1exes.l~ This stereochemistry is also (12) Cromer, D. T.;Waber, J. T.Acta Crystallogr. 1965, 18, 104-109. Stewart, R. F.; Davidson, E. R.; Simpsom, W. T. J . Chem. Phys. 1965, 42, 3175-3187. Cromer, D. T.Acta Crystallogr. 1965, 18, 17-23. (13) Rossi, A. R.;Hoffmann, R.lnorg. Chem. 1975, 14, 365-374.
X
1'
13929 (9) 2859 (2) 330 (2) 2164 (2) 551 (5) 3608 (8) 1608 ( 7 ) 646 (7) -502 (7) 74 (6) 4565 (9) 5630 (8) 2768 (7) 4161 (7) 3256 (8) -1048 (8) 617 (9) 6 2 (8) 3002 (8) 3094 (9) 1248 (8) 7294 (6) 6372 (6) 5994 (7) 6580 (8) 7503 (7) 7866 (7) 7116 (6) 7706 (6) 7231 (7) 6183 (7) 5566 (7) 6062 (6) 8971 (6) 9613 (6) 10703 (6) 11249 (6) 10650 (6) 9539 (6) 7188 (6) 6907 (6) 6588 (7) 6548 (7) 6844 (7) 7163 (6) 7657 (7) 141 (6) 216 (6) 51 (5) -3 (6)
11572 (4) 1183 (1) 1780 (1) 1479 (1) 861 (2) 3019 (3) 498 (2) 702 (3) 413 (3) 668 (3) 3157 (3) 3321 (4) 791 (4) 968 (4) 1715 (4) 1722 (4) 2383 (3) 1877 (3) 1097 (2) 1962 (3) 1720 (3) 1654 (2) 1865 (3) 2310 (3) 2546 (3) 2360 (3) 1924 (3) 827 (3) 791 (3) 585 (3) 426 (3) 462 (3) 660 (3) 1053 (2) 1389 (3) 1327 (3) 927 (3) 575 (3) 644 (3) 909 (3) 450 (3) 266 (3) 551 (3) 1003 (3) 1194 (3) 1108 (3) 24 (2) 48 (2) 82 ( 2 ) 57 (2)
Z
3723 (9) -1951 (2) 398 ( 2 ) -847 (2) 1268 (5) 1377 (8) -167 (7) -916 (7) 2490 (7) 1795 (6) 1710 (9) 2121 (10) 3120 (7) 1771 (7) 2754 (8) -555 (8) 106 (9) 1810 (7) -1455 (7) -363 (8) -2188 (7) 4886 (6) 4183 (7) 4404 (8) 5403 (9) 6088 (8) 5847 (7) 5667 (6) 6869 (6) 7675 (7) 7326 (7) 6163 (7) 5371 (6) 5052 (6) 4726 (6) 4863 (6) 5371 (7) 5680 (6) 5533 (6) 3399 (6) 3158 (7) 2036 (8) 1095 (7) 1297 (7) 2425 (6) 4766 ( 7 ) 42 (6) -54 (6) -157 (5) -79 (6)
consistent with the expected ligand distribution in pentacoordinate d8complexes (ethylene, a 7r-acceptor ligand, and halogens prefer the equatorial positions of the TBP). In Figure 2 is represented the 31P(1H) NMR spectrum obtained when an ethylene atmosphere is maintained in an N M R tube containing a 0.01 M solution of CoBr(PMe,), or CoI(PMe,), in a mixture of deuterated acetone and acetonitrile (1:I ratio). The presence of acetonitrile drastically changes the spectrum. Two species are formed, both stereorigid. No modification in the resonances occurs between -80 and -35 "C. Above -35 "C, the signals are broadened because the diamagnetic species undergo dissociation into paramagnetic molecules (reaction 3 backward and C2H4 dissociation leading to the [Co( MeCN)(PMe,),] Br species), while the solution changes from brown to green. CoBr(PMel)? - .
+
-80 o c
C2H4' +35 "C.MeCN/Me2C0 '
[Co( MeCN)( C2H4)(PMe,),] Br
+
(14) Meier, P. F.; Merbach, A. E.; Dartiguenave, M.; Dartiguenave, Y . J . A m . Chem.Soc. 1976,98,6402-6403. lnorg. Chem. 1979, 18, 610-618. lnorg. Chim. Acta 1980, 39, 19-26.
3894 J . Am. Chem. SOC.,Vol. 104, No. 14. 1982 Table 11. "P(,H} NMR Results (- 80
+
Capelle et al.
5 "C)a JPaP,
compd
Co BrC, H ,KPMe ,1,
solvent me thano 1
6 (Pa)
9.3 d 10.3 d 9.8 d 6.8 d 23.0 t 19.0 d 23.4 t 19.0 d 23.4 t 19.1 d 8.5 t 24.0 q 32 t (br) 17.2 d
acetoneb
8 (P,)
-4.3 t -- 3.6 t -3.6 t -9.1 t -3.8 d
3
Hz
39 39 39 39 59 38
tolueneb methanolb CoI(C,H,)(PMe,), (Co(MeCN)(C,H,)(PMc,), ] BPh, acetonitrile/methanoIb lCo(L)(C,H,)(PMe, ), I BPh, acetonitrile/methanoIb 59 ICo(MeCN)(C,H,)(PMe,),~I acetonitrile/methanolb --4.3 d [Co(L)(C,H,)(PMe,), 1 I acctonitrile/methanoIb -2.2 t 39 59 [Co(MeCN)(C,H,)(PMe,),l Br acetonitrile/methanolb -4.5 d 39 ace tonitrile/rr~ethanoIb [Co(L)(C,H,)(PMe, l 3I Br [Co(C,H,)(PMe,),l BPh, acetoneb 54 3.1 t tolueneC -5.4 d 48 Co(CH,)(PMe,),d CO(CH,)(C,H,)(PM~,),~ tolueneC -9.9 d (br) tolueneC -3.6 t 32 W C , H,)(C, H,)(PMe, ace tonitrilelacetoneb [Co(MeCN),(PMe,),] Br -5.4 s -4.5 s acetonitrilelacetoneb [Co(MeCN), (PMe,), I I acetone [Co(MeCN)(PMe,),]BPh, no signal " A l l chemical shifts expressed in ppm from H,PO,, 62.5%;br =broad, d = doublet, t =triplet, q =quartet. Measured with P(OMe), as reference (6 141 upfield H,PO,, 62.5%),not corrected for temperature. Measured with PMe, as reference ( 6 -61 from H,PO,). Reference 26. e References 6 and I . ~~
+30
+20
0
410
-10
Figure 2. 3'P('HJNMR spectrum of 0.01 M CoBr(PMe,), in a 1 : I (CD,),CO-CD,CN mixture under an ethylene atmosphere ( T = -80 "C), indicating the presence of the two species: [Co(MeCN)(C,H,)(PMe3)3]Brand [CoL(C,H,)(PMeJ,]Br (asterisk).
To the first compound A, characterized by a near first-order A2B spectrum (Jpp= 59 Hz) with a low-field triplet (axial PMe,) and high-field doublet (equatorial PMe,) in the ratio of 1.2, is a t t r i b u t e d t h e trigonal-bipyramidal s t r u c t u r e [Co(MeCN) (C2H.4)(PMe3) 31 (A). +
MeCN
A
In the second species B, displaying a near first-order A2Bpattern with a low-field doublet and a high-field triplet (Jpp= 39 Hz), a trigonal-bipyramidal geometry with two axial and one equatorial PMe, ligands is likely. The two equatorial positions of B may
H
be filled either by one ethylene and one acetonitrile ligand or by two ethylene ligands. Indeed, a diolefin complex was isolated for
~
the isoelectronic Fe(0) compound Fe(CO),(olef), (olef = methyl acrylate),Is whereas recent X-ray work on [Co(MeCN)(diphenylacetylene)(PMe,),] BPh4 showed that acetonitrile, PMe, and the unsaturated ligand are distributed as in B.I6 An N M R spectrum run with a higher concentration of ethylene showed a very slight increase of the [B]/[A] ratio. Although this favors the formulation of B as a diolefin adduct, we do not consider this result as fully conclusive, and both of the above possibilities for B are retained as equally reasonable. An identical 31P(1H)spectrum, showing the presence of both species A and B, is obtained when [Co(MeCN)(C,H,)(PMe,),] BPh,.MeCN (isolated as described below) is dissolved in a l:! acetone-acetonitrile mixture under ethylene at -80 OC. This confirms that the halogen was not present in the coordination sphere when the halide compound was used as the starting material. On the other hand, when the BPh4- salt is dissolved in acetone at -90 O C under ethylene, no signal appears in the )IP N M R spectrum. Thus, in acetone, [Co(MeCN)(C2H4)(PMe3),]+ dissociates to give, as major products, paramagnetic species which have not yet been characterized. Consequently, the formulation of complex B as a diethylene adduct or as an isomer of A with ethylene and acetonitrile in equatorial positions is still uncertain. Species B presents a coupling constant (Jpp= 39 Hz) sensibly lower than A (Jpp= 59 Hz). Thus, one could expect for B a distorted trigonal-bipyramidal structure as observed for Co(C,H,)(Ph)(PMe,),, for which a similar Jppvalue of 32 Hz was found.7 On the other hand, according to Meek et al.,27 in d8 five-coordinateCo( I) compounds, square-pyramidal species exhibit Jppvalues lower than trigonal-bipyramidal complexes. Consequently, it cannot be totally excluded that our low value of Jpp can be related to a square-pyramidal geometry, but we have not retained this possibility in view of the marked preference of pentacoordinate Co(1) compounds with monodentate PR3 ligands for the trigonal-bipyramidal structure. The only information provided by the ' H N M R spectrum between -35 and -80 O C is that there seems to be no intermolecular exchange process between free and coordinated ethylene, the singlet due to free ethylene remaining unmoved at 5.1 ppm. Three broad lines for the PMe, protons and those of coordinated ethylene are observed at 1.1, 1.5, and 2.1 ppm and undergo no appreciable shape modification between -80 and -35 "C. Figure 3 shows the -80 "C 31P('H)N M R spectrum of [Co(PMe3),]BPh4 (0.01 M) in deuterated acetone under ethylene. A diamagnetic stereorigid species is present, displaying a near (15) Grevels, F. W.; Schulz, D.;Koerner von Gustorf, E. Angew. Chem., Ed. Engl. 1974, 13, 534-536. (16) Capelle, B.; Beauchamp, A. L.; Dartiguenave, M.; Dartiguenave, Y., to be submitted for publication.
Int.
(Trimethylphosphine)cobalt(I)Complexes
1‘5
IO
5
0
31P{lH] NMR spectra of 0.01 M [Co(PMe3),]BPh4in (CD3),CO under an ethylene atmosphere: (a) experimental; (b) calculated for A(6(P,) - b(P,)) = 145 Hz, Jpap, = 54 Hz, and band width = 34 Hz Figure 3.
J . A m . Chem. SOC.,Vol. 104, No. 14, 1982 3895 Table 111. Bond Angles (Deg) in the Complex Cation P( 1)-Co-P(2) 108.9(1) Co-P(l)-C(ll) P( l)-Co-P(3) 96.7(1) Co-P(1)4(12) P(l)-Co-N( 1) 90.8(2) Co-P(l)-C(13) P(l)-CO-C(l) 98.1(3) C(ll)-P(l)-C(l2) P( l)-CO-C(2) 138.9(3) C(ll)-P(l)C(13) P(2)
