0 Copyrighf 1995 American Chemical Society
Volume 14, Number 8,August 1995
C'ommunzcatzons Synthesis, Structure, and Reactivity of the Iridium Hydrazido-BridgedComplex
Cesar H. Zambrano, Paul R. Sharp,* and Charles L. Barnes Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211 Received April 20, 1995@
-
Summary: The hydrazido-bridged iridium complex
synthesis, structure, and reactivity of the hydrazido-
Cp*Ir(p-C&&-NC&dIrCp*
bridged iridium complex C P * ~ ~ O L - C ~ H ~ N - N C ~ H ~ ) I ~ C
-
(1;Cp* = CsMed reacts
I
with HZ under pressure with oxidation of the N-N bond to give Cp*IrH(p-C&N=NC&ldHIrCp*
(3) in its cis
and trans forms. I n t h e o f hydrogen, 3 is converted back to 1 with reduction of the N-N bond. Complex 3 reacts with CC13Br to give only the cis isomer of Cp*IrBr(p-C&iV=NCd&)BrIrCp* also prepared by re-dith
(4). Complex 4 is
HBr or Brz.
While there have been many reports involving the preparation and chemistry of early-transition-metal hydrazido complexes,l late-transition-metal derivatives This , ~ paucity of late(groups 9-11) are very ~ c a r c e . ~ metal hydrazido complexes, as well as the potentially rich chemistry that may be expected in these systems, prompted these investigation^.^^ Here, we report the @Abstractpublished in Advance ACS Abstracts, July 15, 1995. (1)(a) Pelikan, P.; Boca, R. Coord. Chem. Reu. 1984,55, 55. (b) Leigh, G. J.ACC.Chem. Res. 1992,25,177.(c) Dilworth, J. R.; Richards, R. L. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford, England, 1982; Chapter 60.(d) George, T.A.; Kaul, B. B.; Chen, Q.;Zubieta, J. Inorg. Chem. 1993,32,1706. (e) Vale, M. G.; Schrock, R. R. Organometallics 1993,12, 1140 and references listed therein. (2)(a) Ashley-Smith, J.; Green, M.; Mayne, N.; Stone, F. G. A. J . Chem. SOC.,Chem. Commun. 1969,409.(b)Hussein, F. M.; Kasenally, A. S. J . Chem. SOC.,Chem. Commun. 1972,3. (c) Ashley-Smith, J.; Green, M.; Stone, F. G. A. J . Chem. SOC.,Dalton Trans. 1972,1805.
0276-7333/95/2314-3607$09.00/0
(1;Cp* = CsMes) in which the hydrazido link contains two ortho-metalated phenyl rings. Three different routes were found for the synthesis of 1 (Scheme 1). The reaction of the lithium salt PhNHNLiPh or PhNLiNLiPh with (Cp*IrCla)zgives low yields of l4along with a second product, Cp*(C1)Ir(v2CGH*N=NPh) Better yields are obtained when 1,2diphenylhydrazine is reacted with iridium complexes bearing basic ligands. Whereas the reaction of PhNHNHPh with Cp*IrN(t-Bu)6 gives 1 in moderate (3)(a) Ramamoorthy,V.;Wu, Z.; Yang, Y.; Sharp, P. R. J . Am. Chem. SOC. 1992,114,1526. (b) Sharp, P. R.; Yang, Y.; Wu, Z.; Ramamoorthy, V. In The Chemistry of the Copper and Zinc Triads; Welch, A. J., Chapman, S. K., Eds.; The Royal Society of Chemistry: Cambridge, England, 1993;p 198. (cl Zambrano, C. H.; Barnes, C. L.; Sharp, P. R. Presented at the 205th National Meeting of the American Chemical Society, Denver, CO, April 1993,INOR 413,and 29th Midwest Regional Meeting of the American Chemical Society, Kansas City, KS, Nov 1994, INOR 130. (4)Data for 1 are as follows. 'H NMR 22 "C, 6 in ppm; aryl ring assignments were made with respect to the ipso C attached to N): 1.46(C&fes),8.47(dd, 2 m-H, 'JHH = 7.4 Hz, 'JHH = 1.5 Hz), 8.16 (dd, 2 o-H, ~ J H=H7.4 Hz, 2 J =~1.6~Hz), 7.17-7.28(m, 4 m- and p-H). l3C{lH}NMR (CsD6, 22 "C, 6 in ppm): 10.6(C&fe5),88.3(CsMes), 164.3,158.8, 136.4,124.4,121.3,120.2 (Ir-c6H,N). UV-vis (35 "c, toluene): idmax) 600 nm ( a = 1.17 x lo4 M-I cm-l), 2 672 nm ( E = 1.10x 104 M-1 cm-I), E. 432 nm ( E = 9.34 x lo3 M-I cm-l). Anal. Calcd for Ir2C32H38N2: C, 46.02;H, 4.59;N, 3.35.Found: C, 45.83;H, 4.64; N, 3.31. (5) See the supporting information.
0 1995 American Chemical Society
Communications
3608 Organometallics, Vol. 14, No. 8,1995
Scheme 1
fi
A
2 Cp*IrNBu'
+ PhNHNHPh
- 2 H~NBU'
E
+ PhNHNHPh
- 4 H20
16-electron, Ir(II1) metal centers bound to nitrogen atoms which may show highly basic properties.ll Because of the nucleophilic character of these atoms, an enhanced reactivity is expected. Unfortunately, reactions of 1 with electrophiles such as CH31, CH303SCF3, and PhCH2C1 have only led to intractable products. Compound 1 reacts with hydrogen under pressure (greater than 200 psi) to give a single product which is
yields, the reaction with [(Cp*Ir)&-OH)3]0H7 produces 1 in yields greater than 90%. Crystals of air-sensitive 1 were grown from hexanelayered THF solutions at -20 "C. An ORTEP view of 1 (hydrogen atoms omitted) is shown in Scheme 1.8The overall structure consists of two Cp"1r fragments bridged by a single 1,2-diphenylhydrazido ligand in which each aryl ring is ortho-metalated to each iridium atom. This binding mode of the hydrazido ligand results in the formation of one edge-shared (N-N) diaza metallacycle ring per metal atom. An important structural feature of this molecule is the N-N distance (1.419 A, averaged), which falls well in the range observed for N-N single b o n d ~ . Also ~ ~ , of ~ importance are the bond angles around each of the nitrogen atoms, which add up to 360". Since this structural feature invokes trigonalplanar nitrogen atoms, some degree of metal-ligand, dn-pn interaction can be conceived. Nevertheless, the iridium-nitrogen bond distances (1.96 A, averaged) are not short compared with other Ir-N amido bonds.1° The apparent lack of Ir-N (dn-pn) interactions result in (6)Gluek, D. S.;Wu, J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1991,113,2041. (7) Bailey, P. M.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1981, 1997. (8)Crystal data for 1: IrC16HlgN.(C&2 N4), monoclinic, with a = 16.7746) A, b = 13.916(3)A, c = 22.343(6) B = 110.415(11Y, and V = 4887.9(22) A3 for 2 = 8, and M, = 786.03, d(ca1cd) = 1.630 g/cm3. Data collection was done with a n Enraf-Nonius 0 - 4 diffractometer using Mo Ka radiation. Two independent molecules of 1, located on inversion centers, were found in the unit cell. Additionally, two molecules of PhNHNHPh of crystallization were found per dimer. The space group was P21/c.Of 7066 measured reflections, 6797 were unique and 5706 had Z > 2.0dZ). The structure was solved by direct methods. The last least-squares cycle gave R = 0.056 and R , = 0.094 with (A/ dmax = 0.004. Selected bond distances (A) and angles (deg) for 1 are as follows. Molecule 1 (ORTEP shown in Scheme 1): Ir(l)-C(3), 2.150(12); -C(4), 2.194(11);-C(5), 2.166(13); -C(ll), 2.020(13); -N(l), 1.956(11); N(l)-N(l)a, 1.402(19); N( l)-Ir(l)-C( 111, 78.5(5); Ir(1)N(1)-C(16)a, 129.2(8);-N( 1)a, 121.5(8);C(16)a-N( l)-N( l)a, 109.2(10). Molecule 2: Ir(2)-C(21), 2.189(14); -C(22), 2.189(12); -C(25), 2.142(12); -C(31), 2.037(12); -N(2), 1.961(11); N(2)-N(2)b, 1.436(21); Ir(2)N(2)-C(36)b, 131.6(9); -N(2)b, 120.5(9); C(36)b-N(2)-N(2)b, 107.8(10) (a and b correspond to atoms across the inversion centers in molecule 1and molecule 2, respectively). (9) (a) Zambrano, C. H.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1994,13,1174. (b) Schrock, R.R.; Glassman, T. E.; Vale, M. G.; Kol, M. J. Am. Chem. SOC.1993, 115, 1760. (c) Matsumoto, K.; Hoshino, C.; Kawano, M. Znorg. Chem. 1992,31,5158.
A,
-
r--
formulated as the iridium-hydride derivative Cp*IrHI
(u-C~H~N=NC~H~)H (3I)~,present C ~ * in two isomeric
forms, cis and trans (Scheme 2).12 lH NMR (CsD6) spectra show two sharp signals at -15.05 and -15.92 ppm, consistent with the presence of iridium hydrides. The integral ratio of these peaks is 0.6:1.0, suggesting that one conformational isomer is dominant. Two distinct Cp* signals and two sets of aromatic peaks, one for each isomer, are also found in approximate ratios of 0.6:l.O. Assignment of a particular NMR resonance to either the cis or trans isomer was not possible, and spin saturation transfer as well as 2D-NOE experiments showed no appreciable isomeric exchange at 300 K.
'
(10)(a) Rahim, M.; White, C.; Rheingold, A. L.; Ahmed, K. J. Organometallics 1993, 12, 2401. (b) Dobbs, D. A.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 3836. (c) Kolel-Veetil, M. K.; Rahim, M.; Edwards, A. J.; Rheingold, A. L.; Ahmed, K. J. Znorg. Chem. 1992,31, 3877. (d) Finke, R. G.; Lyon, D. IC; Noyima, K.; Sur, S.; Mizuno, N. Znorg. Chem. 1990,29, 1787. (e) Fryzuk, M. D.; Li, H.; McManus, N. T.; Paglia, P.; Rettig, S. J.;White, G. S. Organometallics 1992,11,2979. (0 Villanueva, L. A.; Abboud, K. A.; Boncella, J. A. Organometallics 1994,13, 3921 and references cited therein. (11)The trigonal-planar geometry of the nitrogens may be explained in terms of a delocalization of the lone pair over the ortho-metalated phenyl rings.'Of (12)Data for 3 are as follows. 'H NMR (CsD6,27 "C, d in ppm; aryl ring assignments were made with respect to the ipso C attached to N): most abundant isomer, 1.73 (s, Cfles), -15.92 (s, IrH), 8.67 (m, 2 m-H), 8.25 (m, 2 o-H), 7.27 (m, 4 m- and p-H);less abundant isomer, 1.77 (s, Cfles), -15.05 (s, IrH), 8.53 (m, 2 m-HI, 8.20 (m, 2 o-H), 7.18 (m, 4 m- and p-H). 13C{1H} NMR (C6D6, 27 "C, b in ppm): most abundant isomer, 10.41 ( C a e s ) , 93.1 (CsMes), 158.7, 162.9, 134.8, 129.2, 120.4 (Ir-C6H4N); less abundant isomer, 10.37 ( C a e s ) , 92.3 (CsMes), 160.0, 162.3, 135.3, 129.3, 120.6 (Ir-CsH4N). IR (Nujol mull on NaCl plates): N r - H ) 2074 (m, br) cm-I; others, 1442 (SI, 1305 (SI, 1277 (s), 1230 (s), 1107 (s), 1024 (s), 750 (s) cm-I. HRFAB-MS (mle): for C32H40N2~9~1r193Ir, [M + HI+ 837.2521 (calcd 837.2508) for C32H40N21g31r2,[M + HI+ 839.2552 (calcd 839.2529). W - v i s (35 "C, toluene): A(max) 590 nm (6 = 1.03 x lo4 M-' cm-l), 1 362 nm (c = 7.33 x lo3 M-I cm-l).
Organometallics, Vol. 14,No.8, 1995 3609
Communications Scheme 2
+ H2(press)
(1)
H2
cis- and truns- isomers
+ 2 HBr, -H2 (or + Brz)
cis- isomer only
Compound 3 is extremely air sensitive, and isolation of crystals suitable for an X-ray diffraction study has not been possible. Moreover, it is found that over time and in the absence of hydrogen pressure, compound 2 converts back to the starting material 1, with elimination of Ha (by lH NMR). The formation of 3 by hydrogen addition to 1 implies the oxidation of the N-N single bond of the hydrazide bridge. Hence, the conversion of 3 into 1 must involve a reduction of the N=N link a t the expense of hydrogen elimination. This reactivity which involves a facile interconversion between a N-N and N=N fragment in an organometallic system is, to our knowledge, unprecedented.13 The transformation of 3 into 1 was monitored by lH NMR and visible absorption spectro~copy,~ and no intermediates were detected during this process. Furthermore, plots of absorbance and concentration vs time show three linear stages during the transformation, suggesting a complex mechanistic process. Complex 3 can be isolated as a dibromide derivative. Addition of CCl3Br (2 equiv) to hydrocarbon solutions of 3 results in dark violet solutions which contain the bis-ortho-metalated,azobenzene-bridged,dibromo com-
addition to 1 is stereospecific, only the cis isomer is produced. This is corroborated by a single-crystal X-ray diffraction study.15 An ORTEP drawing of 4 (hydrogen atoms omitted) is shown in Scheme 2. The structure consists of two Cp"1r fragments joined by a bis-orthometalated azobenzene bridge.16 Here, the N=N bond length of 1.247 A is very close to that of trans-azobenzene (1.236 A)17and also falls within the range observed in iridium complexes containing metalated azobenzene ligands.16J8 In contrast to complex 1, which possesses a planar hydrazido bridge, the C&N=NCf& linkage in 4 shows significant puckering. The latter may be due to the dramatic shortening of the nitrogen-nitrogenunit on going from a single to a double (N=N) bond. The iridium-carbon (Cp*), -nitrogen, and -bromide bond distances are all normal, and both Cp*IrBr fragments are perfectly eclipsed. Because of their interesting reactivity as well as their unusual structural and electronic properties, complexes 1 and 3 are amenable to further study. In 1,the iridium atoms are presumably electron deficient; therefore, its reaction with Lewis bases may give products with
plex Cp*Brir~-CsH4N=NCsH4)IrBrCp*(4). lH NMR
(15)Crystal data for 4: IrNBrH&gCH2C12, monoclinic, with a = 15.177(5) A, b = 17.516(3)8,c = 14.008(6)A, p = 96.59(2)", and V = 3699(2) A3. For 2 = 8 and M,= 582.38, d(ca1cd) = 2.091 g/cm3. The dimer sits on a 2-fold axis, accompanied by. CH2C12 of crystallization. Data collection was done with a n Enraf-Nonius CAD-4 diffractometer using Mo Ka radiation. The space group was C2/c. Of 2693 measured reflections, 2569 were unique and 2317 had Z > 2.0dZ). The structure was solved by direct methods. The last least-squares cycle gave R = 0.056 and R , = 0.070 with = 0.004. Selected bond distances (A) and angles (deg) for 4: Ir-Br, 2.5274(15); -N1, 2.041(10); -C1, 2.210(12); -C2, 2.263(11); -C3, 2.261(12); -C4, 2.157(14); -C5, 2.188(13); -C16, 2.023(14); N1-Nla, 1.247(21); N1-C11, 1.442(16); Br-Ir-Nl, 89.7(3); -C16, 88.9(3); Ir-N1-Nla, 121.7(9); -C11, 127.1(8);Nla-Nl-C11,111.2(9); Nl-Ir-Cl6,75.1(5); N1-C11-C12, 119.5(11); -C16a, 114.7(11). (16)A related bis-ortho-metalated, azobenzene-bridged dimanganese complex has been reported: Bruce, M. I.; Liddell, M. J.; Snow, M. R.; Tiekink, E. R. T. Aust. J. Chem. 1988,41, 1407. (17) Brown, C. J. Acta Crystallogr. 1966,21, 146. (18)(a)Carroll, J. A.; Cobbledick, R. E.; Einstein, F. W. B.; Farrell, N.; Sutton, D.; Vogel, P. L. Znorg. Chem. 1977,16,2462. (b) Bellon, P. L.; Caglio, G.; Manassero, M.; Sansoni, M. J. Chem. SOC.,Dalton Trans. 1974,897. (c)Van Baar, J. F.; Meij, R.; Olie, K. Cryst. Struct. Commun. 1974, 3, 587. (d) Moreland, J. A.; Doedens, R. J. Znorg. Chem. 1976, 15, 2486. (e)Einstein, F. W. B.; Jones, T.; Sutton, D.; Xiaoheng, Z. J. Organomet. Chem. 1983,244,87.
-
spectroscopy on 4 shows a single resonance for the Cp* group and three sets of multiplets for the aromatic protons of the metalated phenyl rings, suggesting the presence of only one isomer. The 13CNMR spectrum is also consistent with the presence of only one isomer.14 Complex 4 is also prepared directly from 1 by addition of HBr (2 equiv) or Br2. The formation of 4 by Br2 ( 13) Although 1,2-diphenylhydrazine is stable in hydrocarbon solutions under nitrogen (for days at 100 "C), 1,2-diarylhydrazines have been reported to oxidize in air to their azo,form: (a) Pinkus, J. L.; Goldman, L. S. J. Chem. Educ. 1977,54, 380. See also: (b) Coyne, L. M.; Mariner, R.; Rice, A. Langmuir 1991, 7, 1660. (c) Coyne, L. M.; Summers, D. P. Langmuir 1991, 7,1675. (14) Data for 4 are as follows. lH NMR (CD3N02,27 "C, 8 in ppm; aryl ring assignments were made with respect to the ipso C attached to N): 1.78 (s, C&e5), 8.30-8.34 (m, 2 m-H), 7.93-7.97 (m, 2 o-HI, 7.14-7.27 (m, 4 m- and p-H). 13C{lH} NMR (CDBr3,27 "C, d in ppm): 10.3 (C&e5), 93.6 (CsMes), 123.3, 129.4, 131.7, 135.2, 160.2, 162.2 (NCsH4). Anal. Calcd for Ir2C32H38N2Br~:C, 38.63; H, 3.85; N, 2.82. Found: C, 38.85; H, 3.94; N, 2.69.
3610 Organometallics, Vol. 14,No. 8, 1995
Communications
interesting structural features. Also under investigation is the mechanism involving the transformation of 3 into 1.
9221835) instruments. We also thank Dr. W. Wycoff and Dr. H. Jimenez for their help in the spin saturation transfer and NOE NMR experiments.
Acknowledgment. We thank the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, U.S. Department of Energy (Grant No. DE-FG02-88ER1388) for support of this work. We also thank Johnson-Matthey for a loan of IrCly3H20. The U.S.National Science Foundation provided a portion of the funds for the purchase of the X-ray (NSF Grant No. CHE-9011804) and NMR (Grant No. PCM-
Supporting Information Available: Text giving experimental details and spectroscopic data for 1-4, text giving details of data collection and structure solution and tables of atomic coordinates, thermal parameters, and bond distances and angles for 1, 2,and 4,and ORTEP drawings of 2 and 4 (30 pages). Ordering information is given on any current masthead page. OM9502897
