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Organometallics 1995,14, 1104-1106
Selenium Complexes of Permethyltantalocene: Interesting Contrasts with Their Tellurium Analogues Jun Ho Shin and Gerard Parkin" Department of Chemistry, Columbia University, New York, New York 10027 Received November 29, 1994@ Summary: A series of selenium derivatives of permethyltantalocene, which include Cp*zTa($-SedH, Cp*2Ta(Se)SeH, Cp*zTa(Se)H, and Cp*2Ta(Se)I have been prepared. The selenido-iodide complex Cp*2Ta(Se)I exhibits novel reactivity differences with MeMgI and MeLi, to give the selenido-methyl complex Cp*2Ta(Se)CH, and selenoformaldehyde-hydride complex Cp*zTa($-SeCHdH, respectively.
As an extension of our interest in metal-ligand multiple bonding,l we have recently described some studies concerned with terminal tellurido and telluroformaldehyde complexes of permethyltantalocene.2 Specifically, we reported the syntheses of Cp*zTa(Te)H, Cp*zTa(Te)CHs,and Cp*zTa(v2-TeCHz)H(Cp* = v5-C5Mej), i.e. the tellurium analogues of the (i) oxo and formaldehyde and (ii) sulfido and thioformaldehyde derivatives described by B e r ~ a w . ~In - ~this paper, we report the syntheses of the previously unknown members of this series, namely the selenium derivatives Cp*zTa(Se)H,Cp*zTa(Se)CHs,and Cp*zTa(v2-SeCHdH. Furthermore, since organotantalum selenium complexes are not common,6 comparisons with the analogous tellurium system provide a rare opportunity to demonstrate how the chemistry of these complexes varies as a function of the chalcogen. A convenient entry to selenium complexes of permethyltantalocene is provided by the synthesis of the diselenido complex Cp*2Ta(y2-Sez)Hupon reaction of Cp*zTaH3 with elemental selenium at room temperature, in the absence of light (Scheme In the presence of ambient light, however, Cp*zTa(y2-Sez)His smoothly converted to the selenido-hydroselenido complex Cp*zTa(Se)SeH over a period of days (Scheme The transformation to Cp*zTa(Se)SeHmay also be carried out in the dark at 100 "C, although the conversion is accompanied by some decomposition. l).738
l).799J0
Abstract published in Advance ACS Abstracts, February 15,1995. (1)Rabinovich, D.; Parkin, G. J . Am. Chem. SOC.1991,113,59045905. (b) Rabinovich, D.; Parkin, G. J. Am. Chem. SOC.1991, 113, 9421-9422. (c) Rabinovich, D.; Parkin, G. J . Am. Chem. SOC.1993, 115, 9822-9823. (d) Rabinovich, D.; Parkin, G. Inorg. Chem. 1994, 33,2313-2314. (e) Howard, W. A.; Waters, M.; Parkin, G. J.Am. Chem. SOC.1993,115,4917-4918. (0 Howard, W. A.; Parkin, G. J . Am. Chem. SOC.1994,116,606-615. (g) Howard, W. A.; Parkin, G. J. Organomet. Chem. 1994,472, Cl-C4. (h) Kuchta, M. C.; Parkin, G. J. Chem. SOC., Chem. Commun. 1994, 1351-1352. (i) Kuchta, M. C.; Parkin, G. J . Am. Chem. SOC.1994,116, 8372-8373. (2) Shin, J. H.; Parkin, G. Organometallics 1994, 13, 2147-2149. (3) van Asselt, A,; Burger, B. J.; Gibson, V. C.; Bercaw, J. E. J. Am. Chem. Soc. 1986,108, 5347-5349. (4) Parkin, G.; Bunel, E.; Burger, B. J.;Trimmer, M. S.; van Asselt, A.; Bercaw, J. E. J. Mol. Catal. 1987, 41, 21-39. (5) Nelson, J. E.; Parkin, G.; Bercaw, J. E. Organometallics 1992, 11, 2181-2189. (6) For a recent report of organotantalum selenium complexes, see: Tatsumi, K.; Kawaguchi, H.; Tani, K. Angew. Chem. Int. Ed. Engl. 1993,32,591-593. (7) See the supplementary material for complete synthetic details and characterization data. @
Scheme 1
t
I' BO'C
f
H '
P~e3
Cp'*Ta 'SeH
25'C
The formation of Cp*zTa(Se)SeH provides an interesting contrast t o the corresponding tellurium system, for which the ditellurido-hydride derivative Cp*zTa(r2-Te2)H2is stable with respect t o Cp*zTa(Te)TeH under comparable conditions. The facile formation of the Cp*zTa(Se)SeH tautomer for the selenium system is most probably a consequence of both (i) stronger Se-H versus Te-H bonddl and (ii) the increased preference for the lighter element to partake in multiple bonding.12J3 The relationship between Cp*zTa(v2-Ez)Hand Cp*2Ta(E)EH (eq 1) bears analogies with several other (8)A mixture of Cp*2TaH3 (0.27 g, 0.59 mmol) and Se (0.14 g, 1.8 mmol) in benzene (ca. 25 mL) was stirred at room temperature for 3 days in the absence of light. After this period the mixture was filtered, the volatile components were removed in uucuo, and the residue was washed with cold pentane to give Cp*2Ta(q2-Se2)Has a purple solid (0.32 g, 88%). The [Ta(v2-Sez)H1moiety of Cp*zTa(q2-Se2)His characterized by (i) an absorption at 1777 cm-' in the IR spectrum attributable to v(Ta-H), (ii) two 77SeNMR signals at 6 -408 and 54 ppm with lJse-%= 295 Hz, of which the resonance at 54 ppm also exhibits 2 J ~ e - ~ = 19 Hz, and (iii) a signal at 1.42 ppm in the lH NMR spectrum with 77Sesatellites (V&-H = 19 Hz) assignable to [Ta-HI. (9) A mixture of Cp*zTaH3 (0.32 g, 0.71 mmol) and Se (0.17 g, 2.1 mmol) in toluene (ca. 30 mL) was stirred at room temperature for 1 day, without precautions being taken to keep out ambient light. After this period the mixture was filtered and stirred for a further ca. 3-8 days, until only Cp*zTa(Se)SeHwas observed by 'H NMR spectroscopy. The volatile components were removed in uucuo, and the residue was washed with cold pentane to give Cp*,Ta(Se)SeH as a yellow-brown solid (0.33 g, 75%). The [Ta(Se)SeHl moiety of Cp*zTa(Se)SeH is characterized by (i) an absorption at 2250 cm-l in the IR spectrum attributable to v(Se-H), (ii) two W e NMR signals a t 6 -209 and 2363 ppm, of which the resonance at -209 ppm exhibits l J s e - ~= 26 Hz, and (iii) a signal at -3.96 ppm in the 'H NMR spectrum with W e satellites ( ~ J S=~26 -H Hz) assignable to [TaSe-Ill. (10) Other examples of terminal hydroselenido complexes include trans-Pt(PEt3)2(SeH)2,108truns-Pt(PEt&(SeH)H,'OBCp*,Ti(SeH)z (~Js-H = 27 Hz),loband (dppe)Ni(SeH)z.loC (a) Blacklaws, I. M.; Ebsworth, E. A. V.; Rankin, D. W. H.; Robertson, H. E. J . Chem. SOC.,Dalton Trans. 1978,753-758. (b) Bottomley, F.; Chin, T.-T.; Egharevba, G. 0.;Kane, L. M.; Pataki, D. A.; White, P. S. Organometallics 1988, 7, 1214-1221. (c) Schmidt, M.; Hoffmann, G. G. Angew. Chem., Int. Ed. Engl. 1978, 17, 598-599. (11)For reference, the E-H bond energies in H2Se and H2Te are 73 and 64 kcal mol-', respectively. See: Gunn, S. R. J.Phys. Chem. 1964,68, 949-952. (12) (a) Norman, N. C. Polyhedron 1993, 12, 2431-2446. (b) Kutzelnigg, W. Angew. Chem., Int. Ed. Engl. 1984,23, 272-295.
0276-733319512314-1104$09.00/00 1995 American Chemical Society
Organometallics, Vol. 14,No. 3, 1995 1105
Communications systems for which there exist pairs of tautomers of the general types Cp*2Ta(q2-XY)Hand Cp*2Ta(X)YH. Some
- e E = Se, Te
E
C p*,Ta
EH
(11
H
specific examples include (i) Cp*2Ta(q2-ECH2)Hand Cp*2Ta(E)CH3(E = 0, S, Se, Te), (ii) Cp*2Ta(q2-CH2NMe)H and Cp*zTa(NMe)CHs,and (iii)Cp*2Ta(q2-CHzCH2)H and C P * ~ T ~ ( C H ~ ) C H ~ . ~ Both Cp*2Ta(q2-Se2)Hand Cp*zTa(Se)SeH are converted to the selenido-hydride complex Cp*zTa(Se)H upon reaction with PMe3 (Scheme 1).7J4J5 The tellurido-hydride complex Cp*zTa(Te)H was previously synthesized from Cp*2Ta(q2-Te2)Hby a similar method, but, in addition to PMe3, mercury was also required in order to provide a more effective driving force.2 The selenido-iodide derivative Cp*zTa(Se)I is readily obtained by reactions of both Cp*2Ta(q2-Se2)Hand Cp*2Ta(Se)SeH with Me1 (Scheme lh7 Interestingly, however, Cp*zTa(Se)I is not obtained as a product of the reaction of the selenido-hydride Cp*nTa(Se)Hwith MeI, which gives, preferentially, the diiodido-hydride complex Cp*2TaH12.16 Cp*zTa(Se)Iserves as a useful synthetic precursor for other organotantalum selenium derivatives. In this context, Cp*zTa(Se)I exhibits at least two different reaction pathways with alkyllithium and Grignard reagents, which may be regarded t o be a result of attack at either the tantalum center or the selenido ligand.17 The specific pathway followed is a sensitive function of both the alkyl and metal moieties of the [RMI reagent. For example, the selenido-methyl complex Cp*zTa(Se)CH3 is produced by the reaction of Cp*zTa(Se)I with MeMgI, whereas the selenoformaldehyde-hydride tautomer Cp*2Ta(q2-SeCH2)H18 is obtained by the reaction of Cp*2Ta(Se)Iwith MeLi. Moreover, BunLireacts with Cp*zTa(Se)I to give the selenoaldehyde complex Cp*2Ta(q2-SeCHPrn)H,while Bu"MgC1 gives the selenidoalkyl derivative C ~ * ~ T ~ ( S ~ ) B In U "contrast, . ~ J ~ how(13)It is interesting to note that the disulfido-hydride complex of niobium (115-C5Me4Et)zNb(g2-S~)H has been reported to convert to a mixture of (q5-C5Me4Et)zNb(S)SH and (rl5-C5Me4Et)2Nb(tl2-S~)SH at 110 'C.ISa The tantalum disulfido-hydride complex (q5-C5H4But)zTa(qZS2)H has also been prepared, but details of possible isomerization were not r e ~ 0 r t e d . However, I~~ the methyl derivative CpzTa(q2-Sz)CH3has been shown to be converted photochemically to a mixture that contains CpzTa(S)SMe and CpzTa(S)Me.13' (a) Brunner, H.; Gehart, G.; Meier, W.; Wachter, J.; Nuber, B. J . Organomet. Chem. 1993,454,117-122. (b) Bach, H.-J.; Brunner, H.; Wachter, J.; Kubicki, M. M.; Leblanc, J.-C.; Moise, C.; Volpato, F.; Nuber, B.; Ziegler, M. L. Organometallics 1992,11, 1403-1407. (c) Proulx, G.; Bergman, R. G. J . Am. Chem. SOC. 1994,116,7953-7954. (14)The [Ta(Se)Hlmoiety of Cp*zTa(Se)His characterized by signals a t b 8.91 and 2153 ppm in the lH and 77SeNMR spectra, respectively, and an absorption assignable to v(Ta-H) at 1844 cm-l in the IR spectrum. (15)The conversion of Cp*zTa($-Sez)H to Cp*zTa(Se)His reversible, in that addition of selenium to Cp*zTa(Se)H slowly regenerates Cp*zTa(y2-Sez)Hin the dark. (16)Cp*zTaHIz may also be obtained by the direct reaction of Cp*zTaH3 w t h MeI. (17)To a certain degree, the dual reactivity associated with the [Ta=Se] moiety has parallels in the reactions of Cp*zW-O with electrophiles, in which attack may occur at either the d2 tungsten center or the oxo ligand. See: Parkin, G.; Bercaw, J. E. Polyhedron 1988,7, 2053-2082. (18)The [Ta(q2-SeCHz)1moiety in Cp*zTa(+SeCHz)H is characterized by 'H, I3C, and 77SeNMR signals at 6 2.45 (d, 35H-H = 3 Hz), 6 50.5 (t, I J c - H = 143 Hz), and 6 -595 ppm, respectively.
Scheme 2 Cp*zTayCH,*-l /s:
14
MeLi
1
Me3SiCHzLi Cp'?Ta 'CHzSiMe3
llO'C
I *
\I
[ Cp'zTa-SeCH3 ] 1
1
I \
ever, both lithium and magnesium (trimethylsily1)methyl derivatives, LiCHzSiMes and MesSiCHzMgCl, react with Cp*zTa(Se)It o give the selenido-alkyl derivative Cp*2Ta(Se)cH~SiMe3.~ The isolation of only Cp*zTa(Se)CHzSiMe3 from the latter reactions is presumably a consequence of the greater steric interactions that would exist between the SiMe3 group and the Cp* ligands within the selenoaldehyde complex Cp*2Ta(q2-SeCHSiMe3)H. Finally, a further class of reactivity exhibited by Cp*2Ta(Se)I is observed with the secondary and tertiary alkyl derivatives Pr'MgCl, ButMgC1, and ButLi, which yield the selenido-hydride derivative Cp*2Ta(Se)Has a consequence of P-H elimination (Scheme 2). Although mononuclear selenoformaldehyde complexes are known,20the synthesis of Cp*2Ta(q2-SeCH2)Hby functionalization of the terminal selenido ligand of Cp*2Ta(Se)I is of particular significance since Cp*2Ta(q2SeCH2)H could not be isolated by adopting an approach analogous to that used for the preparation of Cp*2Ta(q2-TeCH2)H. Thus, whereas Cp*2Ta(q2-TeCH2)His obtained by the reaction of the methylidene-hydride complex Cp*zTa(CHdH with elemental Te and PMe3,2 the corresponding reaction between Cp*,Ta(CHz)H and elemental Se produced a mixture, of which both Cp*2Ta(q2-SeCH2)Hand Cp*2Ta(Se)Me were only minor components.21 Moreover, in contrast to the tellurium analogue, the selenoformaldehyde moiety adopts an orientation in which the CH2 group is located in the central equatorial position, analogous to the case for Cp*2Ta(q2-ECH2)H(E = 0, S), rather than the lateral position observed for Cp*2Ta(q2-TeCH2)H.2122 The formation of the Cp*2Ta(q2-SeCH2)Htautomer in the reaction of Cp*zTa(Se)Iwith MeLi is a reflection of kinetic control, since Cp*2Ta(q2-SeCH2)His unstable (19)In addition, PhLi and PhMgCl react with Cp*zTa(Se)I to give the spectroscopically characterized derivatives Cp*2Ta(vZ-SeCeH4)H and Cp*zTa(Se)Ph,respectively. (20)Mononuclear selenoformaldehyde complexes include CpRh(PMe3)(q2-CH~Se),20a Os(~2-CH~Se)(CO)z(PPh3)2,20b Os(+CHZSe)(NO)( C ~ ) ( P P ~ ~and ) Z [CpRe(q2-CHzSe)(NO)(PPh3)l+.zod ,~~~ (a) Paul, W.; Werner, H. Angew. Chem., Int. Ed. Engl. 1983,22, 316-317. (b) Headford, C. E. L.; Roper, W. R. J . Organomet. Chem. 1983,244,C53C56. (c) Hill, A. F.; Roper, W. R.; Waters, J. M.; Wright, A. H. J.Am. Chem. SOC.1983,105,5939-5940. (d) McCormick, F. B. Organometallics 1984,3, 1924-1927. (21)It is, however, possible that one of the unidentified products of this reaction is the Se-endo isomer of Cp*ZTa(+SeCHz)H, analogous to the tellurium system. (22)The lateral location of selenium is suggested by the observations of (i) magnetization transfer between the hydride and methylene groups and (ii) a coupling of the selenoformaldehydecarbon atom with the Ta-H group (VC-H = 11 Hz), analogous to the values observed = 7 Hz)Zza and Cp*,Ta($SCHZ)H ( ~ J c - H for Cp*,Ta(q2-OCHz)H(VC-H = 10 HzL5 In contrast, VC-H was not observed for Cp*zTa(q2-TeCHz)H.2 (a) Burger, B. J . Ph.D. Thesis, California Institute of Technology, Pasadena, CA, 1987.
1106 Organometallics, Vol. 14,No.3, 1995
Communications
with respect t o cp*2Ta(Se)CH~.~~ Furthermore, since Cp*2Ta(y2-SeCH2)Honly isomerizes to Cp*zTa(Se)CHs at an appreciable rate a t ca. 110 "C, the formation of Cp*2Ta(Se)CH3in the reaction with MeMgI also presumably reflects kinetic control.24 The isomerization of Cp*2Ta(v2-SeCH2)Hto Cp*zTa(Se)CH3 is a first-order process ( K = 1.5(2) x s-l at 110 "C), and the conversion of the d3 derivative Cp*2Ta(v2-SeCD2)Dis characterized by an inverse kinetic isotope effect (KHIKD = 0.6(1) at 110 "C). By analogy with the formaldehyde and thioformaldehyde derivatives Cp*2Ta(v2-OCH2)Hand Cp*2Ta(v2-SCH2)Hreported by B e r ~ a w , ~ the - ~inverse kinetic isotope effect is indicative of a stepwise sequence involving a preequilibrium with [Cp*zTaSeCHaI,followed by rate-determining a-methyl elimination (Scheme 2).25 The molecular structures of the terminal selenido complexes Cp*2Ta(Se)H (d(Ta=Se) = 2.329(2) A) and Cp*zTa(Se)(CHzSiMes)(d(Ta=Se) = 2.372(1) A) have been determined by X-ray diffraction,26and the Ta-Se bond lengths are similar t o the value in [v4-N(CH2CH2NSiMe&ITaSe (2.3300) A).27,28The organotantalum (23) Cp*zTa(+-SeCHPr")H is also converted to the selenido complex Cp*zTa(Se)Bu" at ca. 120 "C. (24) It should also be noted that the isomerization of Cp*zTa(q2SeCHdH to Cp*zTa(Se)CHs is not catalyzed by MeMgI. (25) Attempts to trap [Cp*zTaSeCHslwith, for example, CO or PMe3 were unsuccessful. (26) Cp*zTa(Se H is monoclinic, P21/n (No. 141, with a = 8.388 2) A, b = 14.030(4) c = 17.407(5)A, p = 103,04(2)", V = 1996(1) and Z = 4. Cp*2Ta(Se)CHzSiMe3is triclinic, PI (No. 2). with a = 8.972: (2) A, b = 9.527(2) A, c = 15.488(3)A, a = 83.55(2)", p = 80.30(2)", y = 78.61(2)", V = 1275(1) As, and Z = 2. (27) Christou, V.; Arnold, J. Angew. Chem., Int. Ed. Engl. 1993,32, 1450-1452. (28) For further comparison, the average Ta-Se bond lengths in [Cp*Ta(Se)3Li3CKTHF)31and [Cp*Ta(Se)3Liz(tmeda)zlare 2.40(1) and 2.41(4) A, respectively.6
1,
k
selenium complexes have also been studied by NMR spectroscopy.' Thus, the terminal selenido complexes are characterized by relatively low field 77Se NMR chemical shifts in the range 6 1990-2363 p ~ m , ~ ~ while the singly bonded Se complexes are identified by high-field chemical shifts in the range 6 +54 to -595 PPm. In summary, a series of selenium complexes of permethyltantalocene, Cp*2Ta(v2-Se2)H,Cp*zTa(Se)SeH, Cp*sTa(Se)R(R = H, Me, Bun, CH2SiMe3, I), and Cp*2Ta(v2-SeCHR)H (R = H, PP), have been prepared. These complexes provide some interesting contrasts to their tellurium analogues. For example, the diselenidohydride complex Cp*2Ta(v2-Se2)H is unstable with respect to the selenido-hydroselenide complex Cp*zTa(Se)SeH,whereas the ditellurido-hydride complex Cp*2Ta(v2-Tez)His stable under comparable conditions.
Acknowledgment. We thank the U.S.Department of Energy, Office of Basic Energy Sciences ( No. DEFG02-93ER14339), and the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research. G.P.is the recipient of a Camille and Henry Dreyfus TeacherScholar Award (1991-1996) and a Presidential Faculty Fellowship Award (1992-1997). Supplementary Material Available: Text giving synthetic details and tables of analytical and spectroscopic data for all new complexes and tables of crystallographic data and figures giving structures for Cp*,Ta(Se)H and Cp*,Ta(Se)(CHzSiMes) (32 pages). Ordering information is given on any current masthead page. OM9409128 (29) For comparison, the NMR signal for [q4-N(CHzCHzNSiMe&lTaSe is observed at 1518 p ~ m . ~ '
