Organometallic chemistry of fluorocarbon acids. Synthesis and

arene)Ru(H)(PPh3)2+ derivatives ... Organometallics 2004 23 (24), 5694-5706 ... Syntheses and Structures of RuCl2(L)(HL) (HL = PhC(NOH)NNPh; z = 1−,...
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Organometallics 1986, 5, 38-47

Organometallic Chemistry of Fluorocarbon Acids. Synthesis and Structural and Dynamic Properties of (r-Arene)RuH( PPh,),' Derivatives A. R. Siedle" and R. A. Newmark Science Research Laboratory, 3M Central Research Laboratories, St. Paul, Minnesota 55 144

L. H. Pignolet chemistry Department, University of Minnesota, Minneapolis, Minnesota 55455

D. X. Wang and T. A. Albright' Chemistry Department, University of Houston, Houston, Texas 77004 Received March 28, 1985

Reaction of H2C(S02CF3)2 with (Ph3P),RuH2in neat arene solvents produces (a-arene)RuH(PPh3).zfHC(SO2CF&-. The lH NMR spectra of these compounds indicate that substituents on the arene ring stabilize one of several ring rotational conformations. Molecular orbital calculations at the extended Huckel level were utilized to explore the structural distortion of the RuH(PPh&+ units in these compounds as well as the dynamics of rotation about the arene-Ru axis. Computations on (arene)RuH(PH&+(arene = benzene, aniline, phenylborane) each showed similar distortions in the tripod portion of the molecule which can be traced to more efficient donation of electron density from the hydride to the metal compared to the phosphine ligands. The structure for each of these model compounds was optimized, and barriers to rotation about the arene-Ru bond were computed. Crystal structure determinations on (r-PhCHJRUH(PP~~),+HC(SO~C [monoclinic, F ~ ) ~ - P2,/a, a = 27.571 (4) A, b = 13.620 (3) A, c = 11.632 (3) A, a = 90°, fl = 94.05 (2)O, y = 90°, 2 = 4, R = 0.0351 and (x-PhCH3)RuH(PPh3),'BPh4[monoclinic,P2,/c, a = 15.814 (2) A, b = 16.816 (2) A, c = 20.988 (7) A, a = 90°, fl = 103.39 (2)O, y = 90°, 2 = 4, R = 0.0651 reveal rotational and metal displacement effects predicted by the calculations. We have previously outlined the reactions of bis(perfluoroalkyisulfonyl)alkanes,exemplified by H2C(S02CF3)2, 1, with organometallic hydrides.,J Generally, the reaction pattern, illustrated schematically in eq 1,consists of proton M-H + H+ MH2+ M+ + H2 (1) +

+

transfer followed, in some cases, by reductive elimination of hydrogen and/or dissociation of ancillary phosphine ligands. Such protonation reactions, when carried out on a preparative scale, are usually conducted in an inert, apolar solvent such as toluene. Toluene, when present in the solvated, saltlike products, is simply incorporated into the crystal lattice. The reactions of (Ph3P),RuH2 with fluorocarbon acids are distinctive in that the hydrocarbon solvent is attacked and emerges bonded to ruthenium in ( T - P ~ C H ~ ) R U H ( P ~This ~P)~ paper + . presents the results of a detailed investigation by NMR, X-ray crystallographic, and theoretical methods of such (a-arene)RuH(Ph,q),+ derivatives and the delineation of restricted arene ring rotation in this class of compounds.

Results and Discussion Synthetic Chemistry. The reaction of (Ph3P),RuH2 with H2C(S02CF3)2in dry, deoxygenated toluene proceeds a t room temperature to give (a-PhCH3)RuH(PPhJ2+HC(SO,CF,),-, 2a, in 58% yield. The nature of the initial protonation product is not established but an intermediate such as (Ph3P),RuH+, may form and subsequently react (1)Camille and Henry Dreyfus Teacher-Scholar 1980-1984;Alfred P. Sloan Research Fellow 1982-1986. (2)Siedle, A. R.; Newmark, R. A.; Pignolet, L. H.; Howells, R. D. J . Am. Chem. Soc. 1984,106,1510. (3) Siedle, A. R.; Newmark, R. A.; Pignolet, L. H. Organometallics 1984,3,855. (4)This cation was originally prepared by hydride abstraction from (Ph,P),RuH, with Ph3C+: Sanders, J. R. J. Chem. SOC.,Dalton Trans. 1973,743.

0276-7333/86/2305-0038$01.50/0

with toluene. This reaction represents, when substituted benzene derivatives are employed as solvents, a general synthetic route to ( a r e n e ) R ~ H ( P P h ~compounds )~+ where the arene is benzene (3a), o-xylene (4a), m-xylene (5a), p-xylene (6a),ethylbenzene (7a), isopropylbenzene (8a), acetophenone (9a), anisole (loa), chlorobenzene (1 la), fluorobenzene (12a), and p-fluorotoluene (13a). These compounds may be regarded as the conjugate acids of the neutral, highly reactive (arene)Ru(phosphine)2materia1s.j NMR chemical shift data for a series of HC(S0,CF3), and Ph4B- derivatives are given in Table I (vide infra). In weakly coordinating solvents such as methanol, (Ph3P),RuH, and H,C(S02CF3), instead produce ( x P~,PC,H,)RUH(P~~P)~+HC(SO~CF~),-, 14a, in which one of the triphenylphosphine arene rings is x-bonded to rut h e n i ~ m . ~ ! ~Compound ,' 2a is a yellow crystalline solid stable to atmospheric oxygen and water and having good solubility in polar solvents such as chloroform, acetonitrile, and ethanol, properties shared by its other arene analogues. The infrared spectrum shows a Ru-H stretching band at 2060 cm-' and characteristic anion bands at 1350 and 1100 cm-l. The metathetical reaction with NaE!Ph4 in the latter solvent provides (x-toluene)RuH(PPh,),BPh,, 2b. In this series of compounds, the tetraphenylborate salts 2b-14b are particularly useful and readily purified by recrystallization from mixtures of dichloromethane and ethanol. Early incentive to study these arene complexes in more (5)Werner, H.; Werner, R. Angew. Chem., Int. Ed. Engl. 1978,17,683. (6)McConway, J. C.; Skapski, A. C.; Phillips, L.; Young, R. J.; Wilkinson, G. J. Chem. Soc., Chem. Comm. 1974,327.Regrettably, a listing of the atomic coordinates in (a-PhPPh,)RuH(PPh&BF, is unavailable

and no detailed comparison with our structural data is possible. (7)Protonation of (Ph,P),RuH(CH3CO2) with fluoboric acid also yields this arene complex: Cole-Hamilton, D. J.; Young, R. J.; Wilkinson, G. J . Chem. Soc., Dalton Trans. 1976,1995.We shall describe elsewhere a survey of the reactions of hydridometal carboxylates with fluorocarbon acids.

0 1986 American Chemical Society

Organometallics, Vol. 5, No. 1, 1986 39

Organometallic Chemistry of Fluorocarbon Acids

Table I. Observed Chemical Shifts (ppm) and Coupling Constants (Hz) of Arene Complexes (Arene)RuH(PPh&+ comulex (arene) salt" solvent 6(H-2) S(H-3) 6(H-4) 6(H-5) 6(H-6) G(RuH) J(PH) Me Jzn Jna 2a (toluene) (toluene) (benzene) (benzene) (o-xylene) (m-xylene) 6b (p-xylene) 7b (ethylbenzene) 8b (isopropylbenzene) 9b (acetophenone) 10a (anisole) 10b (anisole) 1 lb (chlorobenzene) 12b (fluorobenzene)' 13b (4-fl~orotoluene)~ 14a (triphenylphosphine) 14b (triphenylphosphine) 2b 3a 3b 4b 5b

HDS BPh, HDS BPh, BPh, BPh, BPh, BPh4 BPh4 BPh4 HDS BPh4 BPh4 BPh4 BPh4 HDS BPh4

CDzClz CDC13 CDC1, CDC13 CDC13 CDC13 CDC13 CDC13 CDC13 CDC13 CDC13 CDC13 CDC13 CDCl3 CDCl3 CDzClz CDC13

4.66 4.37 5.48 4.96 Me 4.09 4.50 4.16 4.27 5.12 4.72 4.39 4.69 4.71 4.41 4.36 4.68

5.28 4.85 5.48 4.96 4.17 Me 4.50 4.80 5.07 4.40 5.40 4.89 4.60 4.83 4.79 5.14 4.11

6.35 5.59 5.48 4.96 5.35 5.06 Me 5.77 6.34 5.80 5.97 5.20 5.26 4.64 F 6.86 5.89

5.28 4.85 5.48 4.96 5.35 4.75 4.50 4.80 5.07 4.40 5.40 4.89 4.60 4.83 4.79 5.14 4.11

4.66 4.37 5.48 4.96 4.17 5.06 4.50 4.16 4.27 5.12 4.72 4.39 4.69 4.71 4.41 4.36 4.68

-9.22 -9.53 -9.09 -9.36 -9.79

37.8 37.7 37.0 38.2 35.0

-9.99 -9.43 -9.04 -9.59 -9.29 -9.50 -9.26 -9.14 -9.54 -8.67 -8.95

37.6 37.5 37.6 37.7 36.5 36.5 37.9 36.9 37.3 38.3d 38.5d

...

...

2.35 2.11 1.81 1.84 2.18 1.24* 1.34* 2.10 3.59 3.28 1.83

6.0

5.9

6.3

5.8

6.2 6.0 5.5 5.5

5.8 5.6 5.4

"HDS, CH(S02CF3)c,6 3.92 (2a), 4.09 (3a), 4.07 (loa),3.91 (14a). *CH2,6 2.46 in 7b; CH, 6 2.73 in 8b. c19F: 6 -126.3 in 12b and 6 -131.8 in 13b; 3J(HRuF) = 6.4 Hz in 12b and 5.8 Hz in 13b; 3J(FCH) = 4.8 Hz in 12b and 3.6 Hz in 13b; ,J(FCCH) = 3.5 Hz in 12b and 3.0 Hz in 13b. dJ(HP,,,,) = 8.7 Hz in 14a and 9.0 Hz in 14b.

detail came from magnetic resonance data on 2a. NMR Properties. The 200-MHz proton NMR spectrum of 2a in dichloromethane-d2reveals well-separated resonances at 6 4.66 (d, JHH = 6 Hz, 2 H), 5.28 (t, 6 Hz, 2 H), and 6.35 (t, 6 Hz, 1 H)due respectively to the ortho, meta, and para toluene ring protons. The assignments are unambiguous since Horthois strongly coupled only to Hmew The hydride resonance occurs as a triplet at -9.2 ppm (JPH = 38 Hz), and the narrow band 'H-decoupled 31Pspectrum comprises a doublet at 51.8 ppm, confirming the presence of a (Ph,P),RuH moiety. The large chemical shift dispersion for the a-arene ring protons, 1.7 ppm, is unusual in that the shielding range in such complexes is more often on the order of 0.3-0.6 ppm. A closely related example is (a-PhCH3)RuC12(n-Bu3P) in which the arene protons give rise to a multiplet between 5.6 and 4.96 ppm.* In 2a, however, the para proton is highly deshielded and moved out of the range found in q6-arene complexes. Since the toluene ligand in 2a has, by NMR criteria, the same symmetry as the free arene, these data indicate operation of a dynamic process sufficiently rapid on the NMR time scale to make the symmetric protons equivalent with respect to the (Ph,P)2RuHunit. We propose that, as a result of electronic effects, $-toluene in (CH3C6H5)RuH(Ph,P)2f salts is subject to restricted rotation which is describable in terms of a double well potential. According to this scheme, two conformations, A and B, are separated by a

small energy barrier, on the order of several kilocalories per mole. Whether A or B is lower in energy, as well as the magnitude of the difference, will be a function of the electronic properties of the ring substituent X as will be discussed in more detail below. In conformation A, one of the ortho arene protons is in a transoid relationship to the hydride ligand on ruthenium and, since hydride is known to exert a strong trans effect, electron density at the ortho position should be reduced. Consequently, one of the ortho protons is shielded relative to its counterpart (8) Bennett, M. A.; Smith, A. K. J. Chem. SOC.,Dalton Trans. 1974, 233.

on the opposite side of the arene ring and relative to H, and Hmeta.Conversely, in conformation B, Hmeteshould be shielded relative to the other ring protons. Low-temperature lH NMR spectroscopic studies of 2a reveal no apparent reduction in symmetry of the toluene ligand, indicating that A-B interconversion has a very low activation energy. Importently, however, the shift of Hortho decreases from 4.66 ppm at 22 OC to 4.39 ppm at -110 OC while the shift of H, increases from 6.35 to 6.57 ppm over the same temperature range; no change occurs for the shift of Hmek That Horthomoves upfield on cooling while Hpaa moves downfield is indicative of a temperature-dependent conformational equilibrium resulting from the difference in energies of structures A and B; effectively, a Boltzmann-type distribution between A and B obtains and the intrinsic rotational barrier between these is quite low. Similar effects have been observed in (alky1benzene)Cr(CO), c o m p o ~ n d s . ~ JIn~ these, however, the conformational energy difference is associated with steric effects due to bulky alkyl ring substituents rather than with electronic effects as in the present case. In the corresponding benzene complex (a-C6H6)RuH (Ph3P)2+HC(S0,CF3)2-, 3b, barrier(s) to ring rotation are quite low and only a single q6-arene proton resonance at 5.48 ppm is observed. Since an extensive series of closely related arene ruthenium complexes was available, efforts were made to analyze their 'H chemical shifts. To eliminate errors due to effects of variations in solvent and counterions, all the cationic materials were converted to the tetraphenylborate salts and spectra consistently obtained in deuteriochloroform. It is well-known that electron-withdrawing effects and diamagnetic anisotropy of transition metals leads to substantial upfield shifts of the protons in $-arene rings.l'J2 Although it is considered that these upfield shifts are due to an anisotropic effect on the shielding tensor, a precise explanation is not yet available.', Ring substituents on free arenes induce both upfield and downfield shifts due to inductive and resonance effects. Additional, specific deshielding in a complexes is ration(9) Jackson, W. R.; Jennings, W. B.; Rennison, S.C.; Spratt, R. J . Chem. SOC.B 1969, 1214. (10) Jackson, W. R.; Jennings, W. B.; Spratt, R. J. Chem. SOC..Chem. Commun. 1970, 593. (11) Emanuel, R. V.; Randall, E. W.; J . Chem. SOC.A 1969, 3002. (12) Wu, A.; Biehl, E. R.; Reeves, P. C. J . Organomet. Chem. 1971,33, 53.

(13) Maricq, M. M.; Waugh, J. S.; Fletcher, J. L.; McGlinchey, M. J. J . Am. Chem. SOC.1978,100,6902.

40 Organometallics, Vol. 5, No. 1, 1986

Siedle et al.

Table 11. Differences between Chemical Shift (6) of Complex (Arene)RuH(PPh&+ and Chemical Shift (a) of Free Arene after Correction for Arene Substituent Chemical Shifts complex (arene)

2a (toluene) 2b (toluene) 4b (o-xylene) 5b (m-xylene) 6b (p-xylene) 7b (ethylbenzene)b 8b (isopropylbenzene)b 9b (acetophenone) 10a (anisole) 10b (anisole) l l b (chlorobenzene) 12b (fluorobenzene)c 13b (4-fl~orotoluene)~ 14a (triphenylphosphine) 14b (triphenylphosphine) “HDS, CH(S02CF,);.

salta HDS BPh, BPh, BPh, BPh, BPh, BPh, BPh, HDS BPh, BPh, BPh, BPh, HDS BHP,

H-2 -0.59 -0.36 Me -0.50 -0.17 -0.57 -0.47 -0.35 -0.20 0.01 -0.19 0.13 -0.20 -1.11

-0.27

H-3 -0.08 0.01 -0.54 Me -0.17 -0.01 0.28 -0.58 0.03 0.13 -0.21 -0.02 0.37 -0.33 -0.84

H-4 1.07 0.83 0.64 -0.49 Me 1.08 1.65 0.74 0.96 0.77 0.51 0.00 F 1.39 0.94

H-5 -0.08 0.01 0.64 0.01 -0.17 -0.02 0.28 -0.58 0.03 0.13 -0.21 -0.02 0.37 -0.33 -0.84

H-6 -0.59 -0.36 -0.54 0.49 -0.17 -0.57 -0.47 -0.35 -0.20 0.01 --0.19 0.13 -0.20

Me 0.00 -0.24 -0.45 -0.47 -0.12 0.05 0.12 -0.49 -0.17 -0.50 -0.40

-1.11

-0.27

bCH,, 6 -0.07 in 7b and -0.10 in 8b. C19F, 6 -13.2 in 12b and 13b.

&zed by particular conformations of the substituted arene relative to groups attached to the metal.g Arene proton NMR chemical shifts for the new ruthenium compounds prepared in this work are given in Table I. Spectra of derivatives of monosubstituted arenes show three multiplets, a two proton doublet, a two proton triplet, and a one proton triplet, each with J ca. 6 Hz, assigned to the protons ortho, meta, and para, respectively, to the substituent. Spectra of the m- and p-xylene compounds 5 and 6b may also be assigned uniquely from the observed ortho coupling constants. The p-fluorotoluene complex 13b was assigned by assuming that the ortho J(HF) is larger than meta H-F coupling. The spectrum of the o-xylene complex 4b was assigned from an analysis of substituent chemical shifts (vide infra). The arene protons in the a-triphenylphosphine complex 14b showed three poorly resolved triplets having relative areas of 2, 2, and 1. The latter is due to the para proton in the $-arene ring, and the peaks of relative areas two were assigned by spin decoupling the para proton which collapsed the meta proton resonance to a doublet; the ortho proton gives rise to an appareent triplet due to equal H-H and H-P coupling. These chemical shifts contain three effects: the inductive and resonance effect of the substituent(s) on the other protons in the arene ring; the shielding effect of the ruthenium atom; and specific effects due to anisotropy of the (Ph,P),RuH moiety. The latter effect provides information about restricted arene rotation in these compounds, and, on order to extract it from gross chemical shift data, corrections must be made for substituent and metal shielding effects. The first correction was made by subtracting, for each arene proton position, the chemical shift of the free arene from that observed in the ruthenium complex. Subtracting the difference between the chemical shift of the $-benzene complex 3b and free benzene compensates for the shielding effect of the phosphine ruthenium hydride unit. The resulting corrected chemical shifts are given in Table 11. Negative values indicate additional shielding at a given proton position over and above that anticipated from the influence of substituents and a complexation. We shall argue that large changes in these corrected chemical shifts caused by variations in ir-arene substituents reflect an electronic stabilization of the A or B rotational conformations shown above. For monosubstituted benzene derviatives, when the substituent is inductively electron releasing (X = CH,, CzH6,i-C3H7),there is a large shielding of the ortho arene protons and a deshielding of Hparawhich we consider to indicate relative stabilization of conformation A. The fluorine substituent in (7r-C,H,F)RuH(PPh,)2BPh4, 12b, has only a weak

electronic effect and the x-fluorobenzene ring appears to have no strong rotational preference. When the substituent on the a-arene ring is electron withdrawing (Cl, OCCH,, PPh,), significant upfield shifts of the meta ring protons are observed, indicating increased stabilization of conformation B. The chemical shifts in the xylene complexes can be calculated, using simple additivity relationships, from the observed shifts in the toluene analogue, in agreement with results for (arene)Cr(CO), derivative^.'^ For example, the induced shifts in 2a indicate that the ortho, meta, and para effects of a methyl group in the q6 ring, -0.36, +0.01, and +OB3 ppm, respectively, are over twice as large as in the analogous (tol~ene)Cr(CO)~*~ The calculated chemical shift for the protons in the p-xylene complex 6b is the sum of an ortho and a meta effect, or -0.35 ppm. The observed shift is within 0.2 ppm of the calculated value; the calculated shifts in 4b and 5a are also within 0.2 ppm of those observed. They would differ by over 1.0 ppm in 4b if the assignments of H(3,6) and H(4,5) were interchanged. In order to further explore the structure and bonding in (a-arene)R~H(Ph,P)~+ derivatives, X-ray crystal structure determinations of the HC(S02CF,),- and BPh4- salts of the toluene derviative (aPhCH3)RuH(PPhJ2+,2a and 2b, were carried out and are described in the following section.

Descriptions of the Structures The crystal structures of 2a and 2b demonstrate wellseparated [(ir-t~luene)RuH(PPh,)~]+ cations and the HC(S02CF3),-and BPh4- anions, respectively. The shortest interionic contacts are 3.306 (5) for C5-021 in 2a and 3.47 (1) for C 3 A 4 4 F in 2b. These distances are not less than the sum of the appropriate van der Waals radii. The gross structures of the (n-toluene)RuH(PPh&+ cations in both compounds are similar, exhibiting the familiar but here distorted “piano stool” architecture. However, there is a pronounced and important difference in the orientation of the toluene ring with respect to the RuH(PPh& unit. This is readily apparent in Figure 1 which shows projection views of both coordination cores drawn normal to the arene rings as well as fram Table I11 which shows a listing of selected bond distances and angles. In 2a, the Ru-H bond lies away from the methyl group and approximately above the C3-C4 bond, nearly eclipsing C3. In 2b, the Ru-H bond lies toward the methyl group, approximately above the Cl-C6 bond and nearly eclipsing C1. These two orientations correspond to conformations

a

~~

~~

(14)Price, J. T.; Sorenson, T. S. Can. J. Chem. 1968, 46, 515. (15) Graves, V.; Lagowski, J. J. J . Organomet. Chem. 1976, 105,397.

Organometallics, Vol. 5, No. 1, 1986 41

Organometallic Chemistry of Fluorocarbon Acids

Table 111. Selected Distances and Angles 2a 2b Ru-P1 Ru-P~ Ru-C1 Ru-C~ Ru-C~ Ru-C~ Ru-C~ Ru-C6 Ru-C~ Ru-H Cl-C7 C1-C2 Cl-C6 C2-C3 c3-c4 c4-c5 C5-C6 P1-C1A P1-C1B

c4

P2

2a

P2 B ^^

63

c2

P1-c1c P2-C1D P2-C1E P2-C1F wp'

2b

Figure 1. Projection views of the ( T - P ~ C H ~ ) R U H ( Pions P~~)~+ in the HC(SO2CF3),-(A) and BPh4- (B)salts.

B and A, respectively. The two structures are not simply related by rotation of the $-toluene ring, and additional significant structural differences exist. In 2a, the ruthenium atom is not positioned over the center of the toluene ring but is displaced by approximately 0.2 A from the ring midpoint in a direction away from the substituted arene ring carbon atom. Thus, the Ru-C1 and Ru-C6 distances [2.380 (3) and 2.342 (4) A] are significantly longer than the average of the other Ru-C contacts [2.256 (4) A]. In 2b, the ruthenium atom is positioned approximately over the ring midpoint with d(Ru-C),, = 2.267 (9) A, d(Ru-C),, = 2.310 (8) A, and d(Ru-C)~n= 2.236 (8) A. The difference in ring slippage in 2a and 2b is in fact close to that predicted in the calculated conformations B and A, respectively (vide infra). The toluene ring in 2a is slightly nonplanar with C1 and C4 being displaced by 0.020 (4) and 0.023 (4) A, respectively, from the C1-C6 least-squares plane away from the ruthenium atom while C2 and C5 are displaced by 0.015 (4) and 0.017 (4) A, respectively, toward the metal. This distortion corresponds to a folding of the ring about the Cl-C4 vector such that the Cl,C2,C3,C4 and Cl,C4,C5,C6 groupings are planar within experimental error and the dihedral angle between these two planes is 3". The .Ir-arene ring in 2b is planar within experimental error, but in this structure, the errors are larger and a slight ring folding would be unobservable. The C-C bond distances within the toluene rings are similar for 2a [average 1.401 (6) A] and 2b [average 1.39 (1) A] while the ring-methyl C-C bonds are slightly different [Cl-C7 for 2a is 1.493 (5) A and for 2b, 1.55 (1)A]. The Ru-P and Ru-H distances in 2a [2.320 (1)and 1.63 (4) A] and 2b [2.314 (2) and 1.64 (6) A] are the same within experimental error but the P 1RuP2 angle is significantly larger in 2b [100.20 ( 7 ) O ] compared with 2a [95.20 (3)"]. The PRuH angles are the same within experimental error for the two structures. The Ru-C distances reveal a significant structural effect. The bonds which are most trans to the Ru-H vector are lengthened relative to the average Ru-C distance. This is especially evident in Figure 1 where, in 2a, the Ru-CG and, in Zb, the Ru-C4 vectors are

Pl-Ru-P2 P1-Ru-H P2-Ru-H P 1-Ru-C 1 Pl-Ru-C2 P l-Ru-C3 Pl-Ru-C4 Pl-Ru-C5 P 1-Ru-CG P2-Ru-Cl P2-Ru-C2 P2-Ru-C3 P2-Ru-C4 P2-Ru-C5 P2-Ru-C6 H-Ru-C1 H-Ru-C~ H-Ru-C~ H-Ru-C~ H-Ru-C~ H-Ru-C6 C2-Cl-C7 C6-Cl-C7 Cl-C2-C3 c2-c3-c4 c3-c4-c5 C4-C5-C6 C5-C6-C 1 C2-Cl-C6

Distances, 8, 2.320 (1) 2.319 (1) 2.380 (3) 2.285 (4) 2.237 (4) 2.248 (3) 2.254 (4) 2.342 (4) 3.612 (4) 1.63 (4) 1.493 (5) 1.431 (5) 1.394 (5) 1.394 (6) 1.401 (6) 1.385 (6) 1.399 (6) 1.835 (3) 1.844 (3) 1.842 (3) 1.837 (3) 1.841 (3) 1.840 (3)

Angles, deg 95.20 (3) 76 (1) 79 (1) 97.54 (8) 98.92 (9) 124.1 (1) 160.5 (1) 154.0 (1) 119.2 (1) 137.9 (1) 165.3 (1) 134.8 (1) 102.4 (1) 90.3 (1) 105.9 (1) 143 (1) 108 (1) 89 (1) 98 (1) 130 (1) 162 (1) 119.9 (4) 121.4 (4) 120.8 (4) 119.6 (4) 119.4 (4) 121.9 (4) 119.6 (4) 118.6 (3)

2.316 (2) 2.312 (2) 2.288 (9) 2.251 (9) 2.265 (9) 2.310 (8) 2.236 (8) 2.255 (8) 3.50 (1) 1.64 (6) 1.55 (1) 1.41 (1) 1.39 (1) 1.41 (2) 1.40 (2) 1.34 (1) 1.38 (1) 1.825 (7) 1.847 (7) 1.840 (7) 1.845 (8) 1.827 (8) 1.843 (7) 100.20 (7) 77 (2) 78 (2) 128.4 (3) 161.3 (3) 140.4 (5) 106.0 (4) 89.0 (3) 97.8 (2) 124.7 (3) 98.5 (3) 95.1 (3) 117.9 (4) 151.9 (3) 160.3 (3) 88 (2) 108 (2) 143 (2) 162 (2) 130 (2) 99 (2) 122 (1) 122 (1) 122 (1) 119 (1) 117 (1) 125 (1) 120 (1) 116 (1)

the most trans to the hydride (these H-Ru-C angles are each 162") and are lengthened. In 2b, this trans lengthening counters the slippage of the ruthenium atom away from the substituted arene carbon, resulting in a nearly symmetrical ring-metal interaction. In 2a, the ring slippage is quite evident since the hydride is most trans to the ortho arene carbon atom C6. The average Ru-C(arene) bond lengths in 2a [2.291 (4) A] and 2b [2.268 (9) A] are slightly longer than those in the ruthenium arene complexes ( C ~ H ~ ) R U C ~ Z ( P ~ Z and P C(1,4-i-C3H&6H4CH3)H~) RuC1,(Ph,PCH3).16 In these compounds, the Ru-C bonds occur as one set of equivalent short (2.20 A) and one set of equivalent long (2.26 A) distances, the latter in each case (16) Bennett, M. A.; Robertson, G . B.; Smith, A. K. J. Organomet. Chem. 1972, 43, C41. (17) (a) Hoffmann, R. J. Chem. Phys. 1963,39, 1397. (b) Hoffmann, R.; Lipscomb, W. N. Ibid. 1962, 36, 3179, 3489; 37, 2872.

42 Organometallics, Vol. 5, No. 1, 1986

Siedle et al.

being trans to the phosphine ligand. The asymmetry in the arene-metal bonding was attributed to a trans bondweakening property of the teritary phosphine.

Molecular Orbital Calculations Calculations at the extended Huckel level’* were utilized to probe the structural distortions observed in 2a and 2b. Geometric and computational details are given in the Experimental Section. The starting point is a model for the parent compound, (C6&)RuH(PH3),+. The coordinate system and several geometrical variables are shown in 15.

+;

I+

I //

15

Here, 81 is the angle between the z axis and the Ru-H bond, 82 is the angle between the z axis and either of the two Ru-P bonds, and 4 (along with 4 9 is the dihedral angle between the x axis and the the Ru-P bond. In all previously known 18-electron (arene)ML3complexes,lgfll = 82 = 54.7’ and 4 = 330.0’ (@’=210.0’). Therefore, the metal has approximately an octahedral coordination geometry with all L-M-L angles equal to 90”. Furthermore, most complexes are very close to q6 ( r in 15 is 1.41 8, when the C-C bond lengths are 1.41 A). It is obvious from Figure 1 that the ML, unit is significantly distorted from this archetypal “piano stool” arrangement. Independent optimization of 8,, 82, 4, and r for (benzene)RuH(PHJ2+in the geometry shown in 15 gave values of 81 = 61°, 82 = 55’, 4 = 338’ (4’ = 202’), and r = 1.33 A. Thus, this compound is predicted to be slipped slightly away from a symmetric configuration, and, more significantly, the two phosphine ligands are distorted toward the T-shaped geometry evident in Figure l. One might think that this distortion is merely a reflection of the small steric size of the hydrogen atom. However, we consider that an electronic effect must also be operative. Figure 2 presents an interaction diagram for (C&& RuH(PH3),+ in a pseudooctahedral geometry (i.e., 81 = 82 = 54.7’, 4 = 330°, 4’ = 210O). The three filled orbitals of benzene are shown on the left side of the figure. On the right side are the valence orbitals of a RuH(PH,)~+fragment. There is little difference compared to the normal ML3 valence orbitals.20*21 At low and nearly identical energies are la’, la”, and 2a’. These are the remnants of the tzeset in an octahedral level splitting pattern. They overlap with the benzene orbitals to a minor extent in (polyene)ML, complexes20p22and consequently remain nonbonding in Figure 2. A t high energy, the 4a’ fragment orbital is basically a metal s and p hybrid. It stabilizes the (18)Muetterties, E.L.;Bleeke, J. R.; Wucherer, E. J.; Albright, T. A. Chem. Reu. 1982,82, 499 and references cited therein. (19)Albright, T. A.; Hoffmann, R.; Hofmann, P. J. Am. Chem. SOC. 1977,99, 754. (20) (a) Elian, M.; Hoffmann, R. Inorg. Chem. 1975, 14, 1058. (b) Elian, M.;Chen, M. M. L.; Mingos, D. M. P.; Hoffmann, R. Ibid. 1976, 158 1148. (c) Burdett, J. Ibid. 1975,14,375. (21)Albright, T.A.; Carpenter, B. K. Inorg. Chem. 1980, 19, 3092. (22) (a) Radonovich, L. J.; Koch, F. J.; Albright, T. A. Inorg. Chem. 1980,19,3373.(b) Albright, T.A.; Hoffmann, R.; Tse, Y.-C.; DOttavio, T . J . Am. Chem. SOC.1979,101,3801.

Figure 2. An orbital interaction diagram for (benzene)RuH-

(PHJ2+ at the pseudooctahedral geometry.

lowest benzene T orbital xl. The remaining two empty fragment orbitals, 2a” and 3a’, lie at moderate energy. In a ML3complex where the ligands are identical, these levels are degenerate. In the pseudooctahedral configuration of the RuH(PH,)~+fragment, 3a’ lies 0.35 eV higher than 2a”. The reason for this derives from the fact that the hydrogen s orbital is initially higher in energy than the lone-pair hybrid of PH3 before interaction with the metal d orbitals. Since 2a” contains no hydrogen s character by symmetry while that in 3a’ is substantial, interaction between metal d and the ligand cr-donor functions sends 3a‘ to higher energy than 2a”. A further consequence of this perturbation is that 3a’ contains significantly greater electron density at the hydrogen atom position and less at the metal compared to 2a”, which is more localized at the metal. In simplistic terms, the hydrogen behaves more like H+ than a H- ligand, an analogy which will be used below. The empty 2a” and 3a’ orbitals overlap strongly with and stabilize the remaining two filled orbitals of benzene, x2 and x3,respectively. The resultant molecular orbitals, labeled x 2 + 2a” and x3 + 3a’ in Figure 2, are also nondegenerate; r2is stabilized more by 2a” than x 3 is by 3a‘. The reason for this is that 28’’ lies closer in energy to the degenerate 1r2/1r3 set. Furthermore, because of the larger electron density at the metal in Za‘, its overlap with 7r2 is larger than between 3a’ and 7r3. In this geometry, the former is calculated to be 0.2313 and the latter 0.2246. Thus, for energy gap and overlap reasons, 2a” is more strongly involved in bonding to the arene x system than is 3a’. A further consequence of this relationship is that the filled molecular orbital x2 2a” consists of 16.2% 2a” character while there is only 8.1% 3a’ character in x3 + 3a‘. This provides the basis of the explanation of why the two phosphines move apart and approach a T-shaped RuHP, geometry. Notice that, in Figure 2, 2a” is antibonding between Ru and P. As 4 in 15 increases from 330’ (+’decreases from 210°), the phosphine lone-pair functions move toward the

+

Organometallics, Vol. 5, No. 1, 1986 43

Organometallic Chemistry of Fluorocarbon Acids nodal plane at the metal. This causes 28'' to be stabilized, and, therefore, it stabilizes 7rz more as (6 increases than at the pseudooctahedral geometry. Counteracting the stabilization of 7rz 2a" along the distortion coordinate is the behavior of the 3a' level. As 4 increases, 3a' rises in energy and therefore becomes a poorer acceptor. However, since 3a' is less localized at the metal atom, the 7r3 + 3a' molecular orbital is initially not destabilized as much as 7rZ 2a" is lowered in energy. In typical (arene)ML, systems where the three ligands have a more evenly balanced donor ability, the reverse situation occurs: 7r3 + 3a' is destabilized more than 7r2 + 2a is stabilized and a regular piano stool geometry with 4 = 300" and 4' = 210" results. Another way to view this distortion is to consider the hydrogen ligand as H+ interacting with Ru to a much lesser extent than do the phosphines. Consider the hypothetical (C,H,)Ru(PH,), molecule (16). The bonding in this type

+

+

5 4

I

Ru

I

H3P

'\

PH3

16

of 18-electron (arene)MLz complex has been described elsewhere.23 These compounds, as well as their (cyclopentadienyl)MLzcounterparts, are bases.24 There are two high-lying occupied molecular orbitals in 16 which are shown in 17a and 17b. The empty s orbital of a proton,

0

E

Figure 3. A plot of the relative energies vs. rotation angle, l , for

(aniline)RuH(PH,),+and (phenylborane)RuH(PH&+.Here, is defined as the dihedral angle made between the C-N or C-B bond and the Ru-H bonds.

18, will maximize its overlap with 17 when the proton approaches (C6H6)Ru(PH3)z in the direction shown by 19.

/Ru -I

.'-H+

H3P

PH3

19 When the interaction between H+ and 16 or 17 is weak, the phosphines will not bend back much from their original positions. When the interaction becomes stronger, more pyramidalization at R U ( P H ~occurs ) ~ in turn causing 17a and 17b to intermixz5so that a highly directional hybrid orbital is formed which can interact with the s orbital of the proton. The structures 2a and 2b can then be regarded as intermediate cases as the Ru(PPhJ2 moiety is not greatly pyramidalized (cf. Figure 1). Our optimized structure of 15 shows the RuH(PPh,), unit to be slipped 0.08 A away from an idealized q6 position. The energy reduction associated with this distortion is quite small; the difference between the energy computed for r = 1.41 i% (at q6) and r = 1.33 A is only 0.2 kcal/mol. This slippage is connected with the angular distortion of (23) Hofmann, P.Angew. Chem. 1977, 89, 551; Habilitationschrift, Universitat Erlangen (1978). (24) Werner, H. Angew. Chem., Int. Ed. Engl. 1983, 22, 927. (25) Albright, T.A. Acc. Chem. Res. 1982, 15, 149.

the RuH(PH& group and with the fact that the Ru-H and Ru-P bond energies are appreciably different. This is evidenced by the fact that in the ground-state geometries of (C6H6)RuH(PH3)z+ with pseudooctahedral coordination at ruthenium (0, = O2 = 54.74", = 330", $'= 210") and (C6H6)Ru(PH,)?+are calculated to be at the q6 value. In both instances, the potential for such a distortion mode is soft and it requires only approximately 2 kcal/mol to deform the structure to r = 1.33 A. The orbital description given for (C,H,)RUH(PH,)~+ corresponds to the conformation in which the M-L bonds eclipse carbon atoms in the benzene ring. An alternative conformation exists wherein the M-L bonds are staggered and eclipse the C-C bonds, 20. The most stable structure

@ 20

was found to be at the q6 position with 8, = 60°,OZ = 55", 4 = 340°,and (6' = 200". The total energy for it was computed to be a minuscule 0.01 kcal/mol lower than for the eclipsed conformation 14. Here, returning to Figure 3,3a' interacts with aZand 2a" with ir3. Since 7r2 and x 3 are degenerate, these interactions are essentially identical with those described above for the eclipsed conformation. Notice that, again, the R u H ( P H ~group ) ~ is predicted to distort toward a T-shaped geometry for the same reasons given previously. Thus, the barrier to rotation in (C6H6)RuH(PR3)z+ is predicted to be negligible, just as in other (benzene)ML3c o m p l e ~ e s . ~ ~ ~ ~ ~

44 Organometallics, Vol. 5, No. 1, 1986

In the context of the NMR and structural studies reported here, it was of interest to learn how a-donor and r-acceptor substituent groups on the benzene ring would modify the conformational preference of the RuH(PPh,), group with respect to the arene ring. For computational efficiency, we have chosen NH2 and BH2 groups to model a-donor and a-acceptor groups, respectively. In each case, calculations were initially carried out by using an q6 pseudooctahedral geometry and the rotational angle, E , defined as the dihedral angle between the C-R and Ru-H bonds, cf. 21, was varied. Maxima and minima as well as

R = N H 2 , BH2

H3P

21 several points between were then reoptimized by varying 81, 82,4, and 4' (see 14) and slippage of the RuH(PPh,), group from a $ position. The results for (a-ani1ine)RuH(PH&+ are shown in Figure 3a. Two minima were found, A and B, shown in a projection view in 22A and 22B. At

our computational level, they have identical energies. In 22A, the values of 81, 82,4, and 4' do not vary significantly from those given in the benzene system (vide supra). Importantly, while the arene in 22A is expected to exhibit v6 bonding, in 22B, the RuH(PH&+ unit slips 0.2 A from v6 in a direction away from the NH2 substituent. In, $-toluene complexes, the methyl group is also a a-donor. Referring back to Figure 1, the arene conformation in (t~luene)RuH(PPh~)~+BPh,-, 2b, is quite close to that calculated in 22B and like the model structure, the metal is not significantly displaced from the ring sixfold axis. Similarly, the structure of (toluene)RuH(PPh3),+HC(SO2CF,),-, 2a, is conformationally like that of 22A, and, as in the calculational model, the ruthenium is slipped away from the methyl substituent. As indicated by Figure 3, a relatively small barrier, 1.5 kcal/mol, connects the two ground-state conformations. Calculations on the model for an arene complex bearing a a-acceptor, (a-PhBHz)RuH(PH3),+, disclose that this compound also has two energy minima denoted as C and D in Figure 3b and corresponding to the conformations shown in projection view in 23C and 23D. Once again, the RuH(PH,), unit

C

'PH3

PH3

D 23

is distorted toward a T-shaped geometry. In 23C, the phenylborane is v6 bonded while in 23D, the metal is displaced approximately 0.2 A toward the borane group. Conformation C is calculated to be 1.8 kcal/mol more stable than D, and a 4.1 kcal/mol barrier connects the two. The conformational preferences displayed by 22 and 23 are easily rationalized. It has been previously demonstrated in some detail that donor-substituted (arene)ML3 complexes prefer the conformation shown in 24 while for

Siedle et al. those bearing instead acceptor substituents, conformation 25 is preferred.l9sZ5A d6 ML, group possesses three empty L

L

L'

L

24 25 hybrid orbitals whose radial extent toward the arene differs little from 2a", 3a', and 4a' in Figure 2 for the RUH(PH,)~ fragment. Likewise, there are three filled orbitals which match la', la", and 2a' in shape. Therefore, it is not surprising that conformations 22A and 22B match that of 24 while 23C and 23D are close to 25. An orbital analysis of these conformational preferences is totally analogous to the rationale presented e l ~ e w h e r e ' ~for , ~the ~ generalized (arene)ML, system.

Experimental Section NMR spectra were obtained on a Varian XL-200 instrument. Bis[ (trifluoromethyl)sulfonyl]methane, prepared by the method of Koshar and Mitsch,% was the gift of R. J. Koshar, 3M Industrial and Consumer Sector Research Laboratory. Arene solvents were deoxygenated by purging with nitrogen and dried with 4A molecular sieves. (TO~U~~~)RUH(PP~~)~+HC(SO~CF~)