Inorg. Chem. 1991, 30,4043-4047 capability of the N 4 donor atom, this coordination mode is more favorable, as the Rh(lI1) center already contains two very strong a-donating phenyl rings. This work shows that the most favorable coordination mode for the triazole ligands can be changed by the erouns. Furthermore. the ~ nrooerties r ~ of the metal ~ r~ ~~ ~ in all cases ~ ~ r pyridyltriazole ligand remains protonated after coordination to the Rh(ll1) center, which is in contrast to the case of the Ru(bpy)2 analogues. The latter observation is important for determining the reduction potential of the neutral ligand. So far, reliable reduction potentials of the free pyridyltriazole ligand could not be obtained. The correlation of the first reduction potentials between [Ru(L),]" and [Rh(ppy),(L)]+ clearly shows that in all cases a L-based reduction is present for the [ R h ( p p ~ ) ~ ( L ) ] + complexes. indicating that the LUMO in these complexes is centered on the pyridyltriazole ligand. This correlation is of importance for the assignment of reduction waves of [Ru( b p ~ ) ~ ( L ) ]complexes, ~+ when it is not clear whether the reduction nrocesses are bnv based or L based. Finallv. in aereement with ;he measureme% carried out on the [Ru(bdy)2(Lfi2+ complexes, the pyridyltriazole ligands appear 10 have weaker *-acceptor properties compared 10 W-bipyridine. A possible exception is the pyridyltriazole ligand with the nitrophenyl substituent (L7), most likely due to the strong electron-withdrawing power of the ~~
~~~
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4043
substituent. The luminescence observed at 77 K for the [Rh( ~ p y ) ~ ( L )complexes ]+ investigated so far appeared to be rather independent of the a-donor/a-acceptor properties of the chelating ligand L. Except for the case of L = biq,22 a ppy-based H H* emission could ~ ~ be assiened. Aeknawledgment. We wish to thank Mr. S. Gorter for collecting the crystallographic data and C. Erkelens and A. W.M. Lefeber for performing the 300-MHz (COSY) N M R experiments. Finally, we gratefully acknowledge Unilever Research Laboratories for the permission to use their electrochemical equipment. Registry No. 1. 136115-72-5; 2, 136115-74-7; 3, 136115-76-9; 4. 136144-67-7; 5, 136115-78-1;6, 136115-80-5; 6(CH,)&O, 136115-85-0; 7. 136115-82-7; 8, 136115-84-9; L8. 136115-94-1; [Rh(ppy),CI],, 33915-80-9; [Rh(ppy),(LI)]. 136115-86-1; [Rh(ppy)2(L2)], 1361 I S 87-2; [Rh(ppy)2(L3)1, 1361 15-88-3; [Rh(ppy),(L4)]. 1361 15-89-4; IRh(DDvML5)l. 136115-90-7: . IRh(o~vML6)l. 1361 15-91-8; IRh.. .~... .. ..... (ppy),(L7)], lj-8115-92-9; [Rh(ppy),(LS)], 136i 15-93-0; 2-thiophenecarbaxvlic , acid hvdrazide.. 2361-27-5. methvl oicolinimidate. 19547-38-7. Supplementary Material Available: Tables of crystallographic data, parameten. thermai parameten, and band distances and angles for [R~(~~~),(L~)~(PF,).(cH,),co and an ORTEP diagram of [Rh(pp~)~L,]+ (9 pages); a listing of structure factors (6 pages). Ordering information is given on any current masthead page.
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Contribution from the Departments of Chemistry. Univcrsity of Michigan, Ann Arbor. Michigan 48109-1055. and University of Delaware, Newark, Delaware 19716
Synthesis and Structure of (CSH4CH3)Ta(SPh)4 and an EHMO Analysis of Its Distorted Four-Legged Piano-Stool Structure Owen J . Curnow,' M. David Curtis,',' Arnold Rheingold.' and Brian S. Haggerty' Received March 13. 1991
Reaction of ($-C,H,Mc)TaCI, with 4 cquiv of NaSPh at -78 OC gave (I5-C,H,Me)Ta(SPh), (I). Singlc.crystal X-ray cryrtallography shoucd the molecule to have a dirtoncd four.lcggcd pianestool S I N C ~ U Wwith t w o Cp'-Ta-S angles averaging I17.2O and the other two averaging 1 0 4 . P EHUO calculationr on (C,H,)Ta(SH). showed thc distortion to be largcl) electronic in nature a, -ell a, 5houing that cir.ligand interactions in CpML, complcxo cannot be ignored. The Cp-M interaaion also has an cffcci on Cp-'4-L angles. Crtstal data for 1. spacc group P i : 7 = 2; a = 9 817 ( 3 ) . b = 10.458 (3). c = I 5 612 ( 4 ) A; n = 78.78 (2). 8 = 71.98 (2). 7 = 67.59 ( 2 ) " : V = 1404 0 (6) A'. R = 4 22. R. = 4.30 based on 4154 reflections with Fo t 5 d F J .
Introduction Compounds of the formula CpML, have structures described as 'four-legged piano stools". They may also be viewed as square pyramids if the C p ligand is considered to occupy a single cwrdination site. Hoffmann et al. have done an EHMO analysis of the structure of CpML, compounds to rationalize the preference for the four-legged piano-stool structure over other possible conformers.' The major d-orbital interactions are as follow~:I-~ The dAyx orbital is used up in u bonding with the four L ligands. The d, and dyzorbitals are mostly involved with the C p ligand, although some a-bonding interactions with the L ligands are also possible. For 18-electron compounds with ndonating ligands, the HOMO is found to be a H* interaction between the metal d t orbital and the p. orbital on each of the L ligands (1'). The S H O M O is
also a H* interaction, but between the metal d, orbital and the px or pv orbital on each of the L ligands ( I F ) . For a 14-electron compound these MOs will be empty; Le., II* will be the LUMO. The corresponding bonding MOs, I and 11, are found much lower in energy. Poli has recently dscribed the distortions of individual L ligands in terms of the C p M - L angle, He found the distortions to be largely dependent on the r-bonding ability of the ligand, the nature of the ligand trans to it, and the metal electron count. For a tbiolate ligand, SR, the orientation of the R substituent will determine with which d orbital the r-donor orbital of the sulfur atom is able to interact. Hence, an orientation with R directed away from the C p ligand will favor n bonding with the d?orbital, while R oriented into the plane of the four L ligands will favor T bonding with the d s
(I) KubBEek, P.; Hoffman". R.; Havlas. Z. Olgonomerolllcs1982. I , 180. (2) Poli, R. Orgmomerollics 1990. 9. 1892. (3) Krucger. S. T.;Poli, R.;Rheingold. A. L.; Stalcy. D. L. Inorg. Chem. 1989, 28,4599.
'University of Michigan. 'University of Delaware. 0020-1669/91/ 1330-4043S02.50/0
0 1991 American Chemical Society
4044 Inorganic Chemistry, Vol. 30, No. 21, 1991 Table I. Crystallographic Data for CpTa(SPh), (1)
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u = 9337 (3)
A
b = 10.458 (3) A c = 15.612 (4) A CY = 78.78 (2)’ 6 = 71.98 (2)O y = 67.59 (2)O V = 1404.0 (6) A3 z = 2
space group = PI (No. 2) T = 298 K x = 0.71073 A paid = 1.647 g/cm3 p = 44.24 cm-I T(max)/T(min) = 2.367 R(F) = 4.22% R,(F) = 4.30%
Table 11. Atomic Coordinates and Isotropic Thermal Parameters for CPTa(SCnHdA atom X Y z u,” A2 Ta 0.26056 (3) 0.19988 (3) 0.34675 (2) 0.0433 ( I ) 0.1576 (2) 0.3683 ( I ) 0.055 (1) S(1) 0.5106 (2) 0.0675 (2) 0.2180 ( I ) 0.048 (1) S(2) 0.3874 (2) 0.3915 (2) 0.2500 ( I ) 0.056 ( I ) S(3) 0.1331 (2) 0.3983 (3) 0.4302 ( I ) 0.066 ( I ) S(4) 0.2089 (3) C(1) 0.0907 (IO) 0.1609 (IO) 0.4893 ( 5 ) 0.071 (4) 0.2183 (11) 0.0389 (11) 0.4771 (5) 0.075 (5) C(2) 0.4023 ( 5 ) 0.065 (4) C(3) 0.2211 (IO) -0.0189 (9) 0.3709 ( 5 ) 0.057 (3) 0.0931 (9) 0.0666 (8) C(4) 0.1783 (9) 0.4260 ( 5 ) 0.063 (4) C(5) 0.0072 (9) C(6) -0.1412 (IO) 0.2878 (11) 0.4212 (7) 0.090 ( 5 ) 0.2453 (3) 0.066 (4) 0.0404 ( 5 ) C(l I ) 0.7782 (6) -0.0689 0.2063 0.079 (5) C(12) 0.9053 -0.2058 0.2385 0.081 ( 5 ) C(13) 0.9169 -0.2334 0.3095 0.077 (5) C(14) 0.8014 -0.1241 0.3485 0.068 (4) C(15) 0.6743 0.01 28 0.3163 0.051 (3) C(16) 0.6628 0.2670 (5) 0.1330 (3) 0.060 (4) C(21) 0.5254 (6) 0.0593 0.078 ( 5 ) 0.3 179 C(22) 0.6201 0.2419 -0.01 59 0.091 ( 5 ) C(23) 0.6998 0.1150 -0.01 76 0.098 (6) C(24) 0.6850 0.0561 0.069 (4) 0.0641 C(25) 0.5904 0.1401 0.1314 0.049 (3) C(26) 0.5106 0.3972 (7) 0.0652 (4) 0.074 ( 5 ) C(31) 0.2078 (7) 0.3694 -0.01 67 0.109 (7) C(32) 0.2003 0.2912 -0.0172 0.101 (7) C(33) 0.1129 0.2408 0.0642 0.101 (7) C(34) 0.0331 0.1462 0.079 ( 5 ) 0.2686 C(35) 0.0407 0.1466 0.055 (3) 0.3468 C(36) 0.1280 0.4855 (7) 0.3921 (5) 0.106 (7) C(41) 0.4543 (8) 0.5685 0.3464 0.145 (9) C(42) 0.5416 0.2777 0. I26 (9) 0.6686 C(43) 0.4962 0.6857 0.2548 0.182 (15) C(44) 0.3633 C(45) 0.2759 0.6027 0.3006 0.121 (9) C(46) 0.3214 0.5026 0.3692 0.054 (3)
Curnow et al. Table 111. Selected Bond Distances, Bond Angles, and Torsion Angles for Cp’Ta(SC6Hs)$ Bond Distances (A) TaCNT 2.116 (8) Ta-S(I) 2.442 (2) Ta-S( 2) 2.394 (2) Ta-S(3) 2.438 (2) Ta-S(4) 2.470 (3) S(l)-C(l6) 1.785 (4) S(2)-W6) 1.777 (5) S(3)C(36) 1.784 (7) S(94)-C( 46) 1.783 (8)
CNT-Ta-S(1) CNT-Ta-S(3) S(I)-Ta-S(2) S(I)-Ta-S(4) S(2)-Ta-S(4) Ta-S(1)
