摘要:

J. CHEM. SOC. DALTON TRANS. 1990 1543 Ferrocenyl Ligands. Part 1. An Analysis of the Structures of Substituted Ferrocenylphosphines to aid in the Understanding of the Ligand Bonding. The Crystal and Molecular Structure of D if errocenyl phenyl phosph ine t Andrew Houlton, Roger M. G. Roberts,* and Jack Silver" Department of Chemistry and Biological Chemistry, University of Essex, Wivenhoe Park, Colchester C04 3SQ Michael G. 6. Drew" Department of Chemistry, University of Reading, Reading RG6 2AD ~ ~~ The crystal and molecular structure of diferrocenylphenylphosphine PPh [C,H,Fe( C,H,) J2 has been determined. The central phosphorus atom is in a tetrahedral environment with CPC angles less than ideal as expected for the presence of a phosphorus lone pair. The average angle is x 1 OO", which is smaller than the corresponding angle in PPh, and 1 - (1 '-dimethylaminoethyl) -2- (diphenylphos- phino)ferrocene.The causes of such bond-angle distortions are discussed with reference to other related structures and also with respect to the effect on 31P n.m.r. chemical shifts. The nature of the interaction between the phosphorus atom and the ferrocenyl moiety can be understood by considering Mossbauer spectra in conjunction with structural data for ferrocenylphosphines and their quaternised derivatives. Recently we have reported the results of an 57Fe Mossbauer and 3C n.m.r. spectroscopic studies of ferrocenyl-amines and -phosphines.' The results highlighted the difference in the type of interaction of phosphorus and nitrogen with the ferrocene moiety.The lone pair of nitrogen is clearly involved in bonding to the ferrocenyl groups (resulting in a trigonal N atom in the case of triferrocenylamine),' whereas the phosphorus lone pair has no such interaction. Although no other crystal structures of ferrocenylamines exist, the structure of [Fe(qS-CSH4NEt,)- (CO)Br{ PhP(OEt),}] has been determined which contains the (q 5-C5H4NEt,)Fe fragment. Examination of this part of the structure reveals the nitrogen atom to be nearly coplanar with its substituents. The angle of this plane with that of the cyclopentadienyl ring is only 5.3". The CNC angles average 119" (being 120.8, 121.3, and 117.8'). These features are again consistent with the delocalisation of the nitrogen lone pair over the whole C5H4NEt, moiety.The shorter N-C(C5H4) distance of 1.332(4)3 A compared to 1.414(15) %i' for the same distance in triferrocenylamine perhaps reflects the electron-releasing effect of the ethyl groups. In order to gain further insight into the bonding involved in these interesting phosphine ligands we have undertaken a structural study of diferrocenylphenylphosphine (1) the results of which form the basis of this report. Experimental Diferrocenylphenylphosphine (1) and ferrocenyldiphenylphos- phine (2) were purchased from Aldrich Chemicals. Recrystallis- ation from acetone afforded crystals suitable for the analysis of (1). The compounds [PPh{CSH4Fe(CSHS)),IJ[I3] (3) and [PPhz(C,H4Fe(C,H,)}I][13] (4) were prepared according to literature rnethod~.~ Mossbauer data were recorded and fitted as previously described.' CrystalZography.-Crystals were prepared as described above. Crystar data.CI6Hz3Fe2P, (l), M = 347.7, triclinic, space group PI, a = 9.339(8), b = 12.133(12), c = 11.283(13) A, D, = 1.39 F(o00) = 352, Q = 118.6(1), p = 78.0(1), y = 109.1(1)0, U = 1058.2 A3, ~ r n - ~ , 2 = 2, D, = 1.37 g h = 0.7107 x ,p(Mo-K,) = 18.3cm-'. A crystal of approximate size 0.25 x 0.3 x 0.3 mm was set up to rotate about the a axis on a Stoe Stadi2 diffractometer and data were collected via variable-width o scans. Background counts were for 20 s and a scan rate of 0.0333" ssl was applied to a width of (1.5 + sin p/tan 0). 3 501 Independent reflections were measured of which 1838 with I > 30(0 were used in subsequent refinement. The structure was determined by the heavy-atom method.All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in calculated positions and refined isotropically. The structure was given a weighting scheme in the form w = 1/[02(F) + 0.003F2]. The final R value was 0.082 (R' = 0.083). In the final cycle of refinement all shift/error ratios were < 0.30. The final difference Fourier map showed no peaks greater than 0.5e k3. Calculations were carried out using SHELX 766 and some of our own programs on the Amdahl V7 at the University of Reading. Scattering factors and dispersion corrections were taken from ref. 7. Positional parameters are given in Table 1 and selected molecular dimensions in the co-ordination sphere in Table 2. Additional material available from the Cambridge Crystallo- graphic Data Centre comprises H-atom co-ordinates, thermal parameters, and remaining bond distances and angles.Results and Discussion Mossbauer Data.-Mossbauer spectroscopic data are presented in Table 3. As we previously reported,' the ferrocenylphenylphosphines all exhibit smaller quadrupole splittings (q.s.) than ferrocene indicating that electron density is withdrawn from the ferrocenyl groups by the phosphino group. This is perhaps unexpected bearing in mind the lower electronegativity of phosphorus compared to nitrogen. However, backbonding into the empty low-lying phosphorus d orbitals is a characteristic feature in the chemistry of phosphorus. The interaction of ferrocenyl groups with phosphorus and the resulting effect on the reactivity of P has been examined by 7 Supplementary data available: see Instructions for Authors, J.Chem. SOC., Dalton Trans., 1990, Issue 1, pp. xix-xxii.1544 J. CHEM. SOC. DALTON TRANS. 1990 Table 1. Atomic co-ordinates ( x lo4) with estimated standard deviations in parentheses for PPh[C,H,Fe(C,H,)], x 5 325(2) 11 072(2) 8 162(3) 12 318(15) 12 907( 14) 13 331(17) 12 979( 14) 12 354(14) 9 617(15) 9 948( 16) 9 458( 15) 8 851(12) 8 984(13) 5 349(12) 3 835( 15) 3 665( 15) 5 078(12) 6 181(11) 5 983(26) 4 617(23) 4 845( 17) 6 354(19) 7 066( 19) 8 051(13) 6 840( 13) 6 851(16) 8 056(17) 9 241(18) 9 208( 15) Y 2 682(2) 828(3) 2 416(14) 2061(15) 3 165(17) 4 206( 14) 3 716(14) 3 259( 19) 2 104(18) 1 130(16) 1719(14) 3 OlO(14) 289( 10) - 1 620(2) - 506( 13) -1 125(12) -761(11) -3 260(14) - 3 568( 13) -2 945(12) -2 241(14) - 2 396( 14) 157( 10) 2 217(11) 2 795(12) 3 841(13) 4 354(17) 3 802( 15) 2 674( 16) 7 243(2) 8 936(2) 6 816(3) 7 138(14) 7 951(18) 9 160(18) 9 178(15) 7 930(14) 10 615(14) 10 367( 18) 9 084( 17) 8 513(13) 9 476(12) 8 456(11) 8 220( 14) 6 820( 15) 6 181(13) 7 197(11) 5 901(16) 6 608( 16) 7 981(14) 8 130(14) 6 825( 17) 6 613(11) 7 150(13) 6 987( 14) 6 304(16) 5 731(17) 5 864( 14) Table 2.Molecular dimensions (distances in A, angles in ") Fe(1)-C(31) Fe( 1)-C(32) Fe( 1)-C(33) Fe( 1)-C(34) Fe( 1 )-C( 35) Fe(1)-C(41) Fe( 1)-C(42) Fe( 1)-C(43) Fe( 1 )-C(M) Fe( 1)-C(45) Fe(2)-C( 11) Fe(2)-C( 12) 2.O45( 10) 2.037( 12) 2.046( 13) 2.060( 1 1) 2.041( 13) 2.022( 13) 2.033(12) 2.022( 14) 2.004( 13) 2.053( 12) 1.999( 12) 2.011(11) Fe(2)-C( 13) Fe(2)-C( 14) Fe(2)-C( 15) Fe(2)-C(21) Fe(2)-C(22) Fe(2)-C(23) Fe(2)-C(24) Fe( 2)-C( 2 5 ) P-C(24) P-C(51) P-C(35) C( 24)-P-C( 35) 100.0( 5 ) C( 35)-P-C(5 1) C(24)-P-C(51) 98.6(5) 2.031(15) 2.054( 13) 2.026( 12) 2.052( 13) 2.023( 15) 2.042( 14) 2.044( 12) 2.029( 1 1) 1.823( 13) 1.81 2( 10) 1.843( 11) 10 1 .O( 5) Table 3.57Fe Mossbauer spectroscopic data (at 80 K) Compound 6/mm s-l A/mm s-l Ref. (1) pph CC ,H,Fe(C SH 511 2 0.52( 1) 2.32( 1) 1 (2) PPh 2 [C,H,Fe(C,H 0.52(1) 2.31(1) 1 (5) [Fe(CsH,PPhd,] 0.53( 1) 2.30( 1) 1 [Fe(C,Hs)2] OS4( 1) 2.37( 1) 1 (3) [PPh{C,H4Fe(C,H,)},I][I3] 0.52(1) 2.27(1) This work (4) [PPh,{C,H,Fe(C,H,)}I][I,] 0.52(1) 2.25(1) This work McEwen et aL83' They reported the pronounced deactivating effect of a ferrocenyl group on an adjacent phosphorus atom in the alkaline hydrolysis of quaternary phosphonium salts.They cited this as evidence for strong interaction between the ferrocenyl group and the cationic phosphorus atom which decreased the electrophilic reactivity of the latter, steric effects having been ruled out. The decreased reactivity of the ferrocenylphosphonium hydroxides compared to the phenyl Figure 1. Ferrocenyl ha, orbital. The 'cored apple' orbital analogue was attributed mainly to the result of overlap of the ha, molecular orbital of the ferrocenyl group with 3d orbitals on phosphorus. From their data the rate-depressing effect of a single ferrocenyl group was almost as great as that of two or three such groups implying that there was effective overlap of just one ferrocenyl h,,orbital with a 3d orbital of phosphorus in the phosphonium cation, which seems to us surprising as there is no obvious orbital symmetry constraint for this.The ferrocenyl ha, orbital (Figure 1) is a molecular orbital (m.0.) that has largely been ignored by workers in the field since the calculations of Moffit.' The iron orbitals that contribute to this m.0. are 4s and 3dzz orbitals. Unfortunately, this orbital combination has not been considered for its contribution to the 57Fe Mossbauer effect. As the only component orbital of the ha, m.0. that can generate a field gradient is the dz2 orbital, it could reasonably be assumed that removal of electron density from this orbital (due to overlap with P) would cause an increase in the q.s. since it has a negative contribution to the field gradient.Therefore based on the hypothesis of McEwen et al., a reaction producing a cationic P should increase the q.s. This is not observed experimentally as can be seen from the parameters of [PPh{C5H4Fe(CsH5)),I][13] (3) and [PPh,(C,H,Fe- (CsH5)}I][13] (4) which show a decrease from the parent phosphine. Structural Data.-The molecular structure of PPh[C,H4- Fe(C,H,)], (1) is shown in Figures 2 and 3 and consists of discrete units of the molecule. The two ferrocene groups have an eclipsed geometry (see Figure 2) with the two rings in each ferrocene approximately parallel (angles of 2.1" between rings I and 2 and 1.6" between rings 3 and 4). The substituent ferrocenes are approximately perpendicular to each other with an angle of 86.9" between the molecular axes of the ferrocene moieties.There are no intramolecular distances significantly less than the sum of the van der Waals radii. All bond lengths are typical of a substituted ferrocene ' ' with Fe-C averaging 2.029(12) 8, to the unsubstituted cyclo- pentadienyl rings and 2.039(12) 8, to the substituted rings. The C-C bonds of the C5H, rings are in the range 1.371-1.474 A. However, the errors in the C-C bonds are such that it is impossible to differentiate average lengths between the substituted and unsubstituted rings unlike our findings in other ferrocene structures,' although a similar trend is apparent. The central phosphorus is in a tetrahedral environment with CPC angles less than the ideal angle of 109.5", being 101.0(5), 98.6(5), and 100.0(5), averaging to 100".The phosphorus atomJ. CHEM. SOC. DALTON TRANS. 1990 1545 n W Figure 2. Drawing of the molecular structure of PPh[CSH,Fe(C,H,)], (1) showing the numbering scheme U Figure 3. Molecular structure of compound (1) showing the eclipsed conformation of the ferrocenyl groups is located (distance rp) 0.85(1) 8, from the plane of the three bonding carbon atoms. The phosphorus is closely planar with the C5H, ring to which it is attached, being 0.06(1) 8, from ring 2 and 0.08(1) 8, from ring 3. Comparison of the structure of PPh[C,H,Fe(C,H,)] with relutedstructures. It can be seen from the figures that the general features of the structure of compound (1) are remarkably similar to those of l-(l'-dimethylaminoethyl)-2-(diphenylphosphino)- ferrocene (6).13 particularly with regard to the orientations of the phenyl and ferrocenyl groups.For the latter, the planes of the phenyl groups lie almost orthogonal to those of the cyclopentadienyl rings of the ferrocenyl substituent. In the case of (l), one ferrocenyl and one Ph group are approximately orthogonal to the second ferrocenyl group. Replacing one Ph by a ferrocenyl group has relatively little effect on the overall geometry. Table 4 lists selected bond lengths and angles for ferro- cenylphosphines and related structures. The average P-C(ferro- cene) distance of 1.817(11) 8, in (1) compares with 1.802(7) A for the corresponding distance in (6). The P-C(pheny1) distance of 1.843(11) 8, compares with an average distance of 1.837(8) A in (6).Both phosphines show P-C(ferrocene) distances shorter than P-C(pheny1) distances, and this latter distance increases with increasing ferrocenyl substitution {cf: mean values: PPh,, 1.828; PPh, C,H,Fe(C,H,)], 1.837; and PPh[C,H,Fe(C,- McEwen et uL8 have reported the crystal structure of benzylferrocenyldiphenylphosphonium chloride. The P-C bond length to the ferrocenyl group, at 1.768(3) 8, is shorter than the other P-C (aromatic) bond lengths, at 1.803(3) and 1.804(4) A, in common with the ferrocenylphosphine derivatives discussed above. These workers suggested that this is due to a de- localisation of positive charge into the ferrocene system by overlap of the ha, orbital with the dzz orbital on P. As discussed earlier, the Mossbauer studies do not support this theory.It is possible, however, to account for this difference from a knowledge of the difference in hybridisation of the phosphorus- bearing carbons in five- and six-membered rings. Simple calculations'4 indicate a 10% increase in s character of the P-C(ferrocene) bond compared with the P-C(pheny1) bond, which would account for a shortening of this magnitude (=0.02 8,). Evidence in support of this comes from a comparison of the C-CH, bond lengths in hexamethylbenzene and decamethyl- ferrocene l 6 of 1.53 and 1.502 8, respectively. Complexation of a metal to a carbocyclic ring also causes some shortening of the exocyclic bonds as is shown by the C-CH, bond distances in [Fe(?16-C6Me&] [tcnq] (tcnq = tetracyanoquinodimethin- view of this and the Mossbauer data for compounds (3) and (4) (from Table 3), it is more likely that donation of charge by the ferrocene moiety to the phosphorus is by ferrocenyl el ring- based orbitals with concomitant increase in back bonding from Fe to C5H5 uiu e2 orbitals.There is also the possibility of some direct overlap between iron e2 and phosphorus d orbitals. It must be stated that the distance between Fe and P has a range of 3.397 8, [in (S)] to 3.581 8, [in (9)], and averages 3.425 8, in (1). These distances are clearly too long for a direct bonding overlap of P and Fe orbitals ( c j normal Fe-P bonds around 2.40 A, although longer distances as high as 2.77 8, have been reported as bondinglg) but could still allow some interaction. For all the compounds (1) and (6)-(9) the phosphorus atom is in a distorted tetrahedral environment with angles (8) less than the ideal angle of 109.5' and this is true for all the unco- ordinated phosphines in (l), (a), and (7).The average value of 8 in these three compounds decreases with increasing ferrocenyl substitution, being reduced from 103.0" in (7) to 101.8' in (6) to 100.0' in (1). This trend may be explained on the basis of valence-shell electron-pair repulsion (VSEPR) theory. The phosphorus lone pair will repel the bonding-pair electrons to a greater extent than the bonding pairs repel one another. Thus increasing the lone-pair character present on the phosphorus causes the angles to be reduced from those of a perfect tetrahedron. The decrease in the CPC angle is in keeping with the electron-donating nature of the ferrocenyl group compared to phenyl in the solid state and is in keeping with Mossbauer data.' As phenyl groups are replaced by ferrocenyl groups, the phosphorus retains more lone-pair character and hence there will be an increase in the repulsion of the bonding pairs and a decrease in the CPC angle.In addition, the ferrocenyl group has a greater electron density on its rings in the 7t cloud than the phenyl group. Thus Hs)]~, 1.843 a >. ide), 1.505(7) and [CO(T16-C6Me6)2]PF6, 1.519(6) A.18 In1546 J. CHEM. SOC. DALTON TRANS. 1990 Table 4. Bond lengths (A) and angles (") of ferrocenylphosphines and relevant structures a Distance (rp) from 3C Compound P-C( ferrocene) P-C( phen y 1) C-P-C( mean) plane( A) Fe-P Ref. PPh, PPhz{C5H,FeC5H,[CH(NMe,)Me]} pph[C 5 H,Fe(C5H5)] - 1.82gb 102.96 0.785 - C 1.802(7) 1.837(8) 1 0 1.8(4) 0.8 10 3.408( 3) 13 1.81 7( 11) 1.843( 11) 100.03 0.85 3.423( 11) This 3.427( 11) work 1.763 - 110.93 0.543 3.468 4 3.397 3 452 3.58 1 1.805 1.816 106.2 0.69 1 3.506 30 1.768 1.804 107.7' - 3.449 8 a Data obtained from the Cambridge Crystallographic Structure Data Base except where indicated to the contrary.Average. ' J. J. Daly, J. Chem. SOC., 1964, 3799. 1 -( l'-Dimethylaminoethyl)-2-(diphenylphosphino)ferrocene. ' From ref. 8. greater repulsion will occur between the phosphorus lone pair and the C5HS group than that for the phenyl group though overall this will admittedly be small. The related distance of the displacement of the phosphorus from the plane of the three bonding carbon atoms is in accord with the observed 8 values. This distance (r,) is shorter for (7) at 0.785 A and increases to 0.85 A in (1). Using simple hybridisation arguments, increase in 8 in going from compounds (1) to (2) to (7) should result in more s character in the P-C bonds and hence more p character in the lone pair.,' This predicts that the ligand strengths should increase in the order PPh3 > PPh,[C,H,Fe(C,H,)] x [Fe- (C,H,PPh,),] > PPh[C,H,Fe(C,H,)],.This sequence has been verified experimentally using ligand displacement in [Ni(a~ac)~] (acac = acetylacetonate),2' though the authors invoke steric hindrance as the dominant effect. Correlation of solid-state and solution structures is fraught with difficulty. However, evidence for such correlation can in some cases be obtained from n.m.r.spectroscopy. In this context, it is interesting to compare the values of 8 with the 31P n.m.r. chemical shift [S(P)]. From a study of trialkylphosphines, Mann22 concluded that an increase in 8 resulted in deshielding of the P nucleus. However, Quinn and Breen 23 have argued that a,p, and y substituent effects of an aliphatic chain also affect S(P).,, For the phosphine series PPh,, PPh,[C,H,Fe(CSH,)], PPh[CSH,Fe(CSH,)],, none of these effects is present. The 6(P) values' are -7, - 15, and -27 p.p.m. respectively (average values). The ground-state electronic properties of the ferrocenyl group are quite similar to those of the phenyl group.,' This is apparent from the Mossbauer data quoted above and also from the almost identical 13C n.m.r.chemical shifts for the C5H5 and Ph carbons in PPh,[C,H,Fe(C,H,)] and PPh[C,H,Fe(C,H,)],.' The values of 8 must therefore be dominated by the stereoelectronic factors previously discussed. The variation of 8 with 6(P) is linear for the above phosphine series, though of course more points are required to be statistically significant (particularly relevant would be data for triferrocenylphosphine which is not available at present). Nevertheless the trend supports Mann's postulate 22 that a decrease in 8 causes an upfield shift of phosphorus resonance. This increased shielding can be rationalised in terms of increasing s-electron density in the lone pair on phosphorus. In this connection, it is also worth noting that the 'J(P-C) values for the ips0 phenyl carbons also increase with 8 and it is tempting to explain this again as being due to increased s character in the P-C bonds.However, it has clearly been demonstrated that 'J(P-C) for PPh, is negative 26*27 which poses serious difficulties for the Fermi-contact theory of coupling p h e n ~ m e n a . ~ ~ . ~ ' The overall evidence from n.m.r. data does however point towards a similarity in the relative geometries of these phosphines in the solution and solid phases. As would be expected, on co-ordination the CPC angle increases since a lone pair becomes a bonding pair. This can be seen in the structures of compounds (8) and (9) (see Table 4) which have 8 values of 110.9 and 106.2" respectively, i.e. closer to the ideal tetrahedral angle. In the latter compound the iron-acyl distance is considered to be normal3' and hence it can be concluded that there is little strain caused by the presence of this structural feature. Hence compound (9) can be considered as a co-ordinated diferrocenylphenylphosphine. The displacement (Y ) of the phosphorus atom decreases from 0.85 A in (1) to 0.691 APin (9).Also the P-C(ferrocene) bond length decreases by xO.12 A. This decrease on co-ordination appears to be quite general as can be seen from structures of 1,l'-bis(dipheny1- phosphino)ferrocene and its metal complexe~.~ *32 As increased ferrocenyl substitution has been shown to increase the lone-pair character of the phosphorus, it would be interesting to solve the structure of triferrocenylphosphine which should exhibit the smallest CPC angles of all such derivatives.Acknowledgements We thank A. W. Johans for his assistance with the crystallographic investigations and the award of an S.E.R.C. studentship to one of us (A. H.). References 1 A. Houlton, P. T. Bishop, R. M. G. Roberts, J. Silver, and M. Herberhold, J. Orgunomet. Chem., 1987,364,381. 2 M. Herberhold, M. Ellinger, U. Thewalt, and F. Stollmaier, Angew. Chem., Int. Ed. Engl., 1982,21,74; Angew. Chem. Suppl., 1982,98. 3 P. Brun, P. Vierling, J. G. Ross, and G. L. Borgne, Organometallics, 1987,6, 1032. 4 G. V. Gridunova, V. E. Shklover, Yu T. Struchkov, V. D. Vil'Cherskaya, N. L. Podobedova, and A. I. Krylova, J. Organomet. Chem., 1982,258,297. 5 M. Y. Hamed, R. C. Hider, and J. Silver, Inorg. Chim. Acta, 1982,66, 13. 6 G.M. Sheldrick, SHELX 76, Package for Crystal Structure Determination, University of Cambridge, 1976. 7 'International Tables for X-Ray Crystallography,' Kynoch Press, Birmingham, 1974, vol. 4.J. CHEM. SOC. DALTON TRANS. 1990 1547 8 W. E. McEwen, C. E. Sullivan,and R. 0. Day, Organometallics, 1983, 9 W. E. McEwen, A. W. Smalley, and C. E. Sullivan, Phosphorus, 1972, 2,420. 259. 10 W. Moffit, J. Am. Chem. Soc., 1954,76,3383. 11 M. I. Bruce, in ‘Comprehensive Organometallic Chemistry,’ eds. G. Wilkinson, F. G. A. Stone, and E. W. Abel, Pergamon, Oxford, 1982, vol. 9, p. 1294 and refs. therein. 12 R. M. G. Roberts, J. Silver, B. M. Yamin, M. G. B. Drew, and U. Eberhardt, J. Chem. SOC., Dalton Trans., 1988, 1549. 13 F. M. B. Einstein and A. C. Willis, Acta Crystallogr., Sect. B, 1980,36, 39. 14 W. A. Bingeland W. Luttke, Angew. Chem., Int. Ed. Engl., 1981,20,899. 15 L. 0. Brockway and J. M. Robertson, J. Chem. SOC., 1939,1324. 16 D. P. Freyberg, J. L. Robbins, K. N. Raymond, and J. C. Smart, J. 17 M. D. Ward and D. C. Johnson, Inorg. Chem., 1987,26,4213. 18 M. R. Thompson, C. S . Day, V. W. Day, R. I. Mink, and E. L. 19 M. Clemance, R. M. G. Roberts, and J. Silver, J. Organornet. Chem., Am. Chem. SOC., 1979,101,892. Muetterties, J. Am. Chem. SOC., 1980, 102, 2979. 1983,243,461. 20 J. F. Nixon and A. Pidcock, Annu. Rer. NMR Spectrosc., 1969,2,345. 21 J. C. Kotz and C. L. Nivert, J. Organomet. Chem., 1973,52, 87. 22 B. E. Mann, J. Chem. SOC., Perkin Trans. 2, 1972,30. 23 L. D. Quinn and J. J. Breen, Org. Chem. Res., 1973,5, 17. 24 See also, D. G. Gorenstein, Prog. Nucl. M a p . Reson. Spectrosc., 25 R. M. G. Roberts, J. Silver, and B. Yamin, J. Organoniet. Cheni., 1984, 26 J. Jakobsen, T. Lund, and S. Sorensen, J. Magn. Reson., 1979,33,477. 27 T. Bundgaard and H. J. Jakobsen, Acta Chem. Scand., 1972,26,2548. 28 N. Muller and D. E. Pritchard, J. Chem. Phys., 1959,31,768, 1471. 29 H. M. McConnell, J. Chem. Phys., 1956,460. 30 I. R. Butler, W. R. Cullen, and S. J. Rettig, Organometallics, 1987, 6, 31 U. Casellato, D. Ajo, G. Valle, B. Corrain, B. Longato, and 32 I. R. Butler, W. R. Cullen, T. J. Kim, S. J. Rettig, and I. Trotter, 1983, 16, 1. 270, 22 1. 872. R. Graziani, J. Crystallogr. Spectrosc. Res., 1988, 16, 583. Organometallics, 1985,4972. Received 1st September 1989; Paper 9/03731D

ISSN:1477-9226    

DOI:10.1039/DT9900001543

出版商:RSC    

年代:1990

数据来源: RSC