J . Am. Chem. SOC. 1988, 110, 6096-6109
6096
Synthesis, Structure, and Reactions of Chiral Rhenium Vinylidene and Acetylide Complexes of the Formula [ ($-C5H5)Re( NO)( PPh3)(X)]"': Vinylidene Complexes That Are Formed by Stereospecific C, Electrophilic Attack, Exist as Two Re=C=C Geometric Isomers, and Undergo Stereospecific C, Nucleophilic Attack Dwayne R. Senn," Andrew Wong,lbAlan T. Patton,'a,bMarianne Marsi,lb Charles E. Strouse,lband J. A. Gladysz*~'"-' Contribution from the Departments of Chemistry. University of Utah, Salt Lake City, Utah 84112, and University of California, Los Angeles, California 90024. Received December 21. 1987
Abstract: Sequential reactions of acyl complexes (~5-C5H5)Re(NO)(PPh,)(COCH,R) (2: R = H (a), CH, (b), C6H5(c), I-naphthyl (d)) with (CF3S02)20(0.5 equiv), base (1.0 equiv), and (CF3S02)20(0.5 equiv) give vinylidene complexes [(q5-C5H5)Re(NO)(PPh,)(=C=CHR)]+CF3S0,(3a-d CF3S03-,63-95%). Complexes 3b-dCF3S03- crystallize as (95 f 2):(5 f 2), >99:1, and >99:1 mixtures of sc/ac Re=C=C geometric isomers but equilibrate to (50 f 2):(50 f 2), (80 f 2):(20 f 2) and (80 f 2):(20 f 2) mixtures in CD2CI2. Photolysis gives (50 i 2):(50 f 2) photostationary states. An X-ray crystal structure of sc-3dPF; ( R d , 1.840 (17) A) shows a P-Re-CgC,, torsion angle of 161S o ,placing the naphthyl substituent anti to the bulky PPh, ligand. Reactions of 3a-dCF3S0,- with base give acetylide complexes (qS-C5H5)Re(NO)(PPh,)(C=CR) (6a-d, 59-93%). Reactions of 6b-d with CF3S03H (-78 "C, assayed by NMR) give (98 f 2):(2 f 2), >99:1, and >99:1 mixtures of ac- and sc-3WCF3SO PPh3 > Table 11. Refinement, described in the Experimental Section, NO > =C=CHR. (c) Compounds not indicated to be specific Re=C=C yielded the structure shown in Figure 2. Positional parameters, isomers are mixtures of isomers. (d) TMP = 2,2,6,6-tetramethylpiperidine. bond distances, and bond angles are summarized in Tables 111-V. (e) dppe = Ph2PCH2CH2PPh2.
J . Am. Chem. SOC., Vol. 110, No. 18, 1988 6099
Rhenium Acetylide and Vinylidene Complexes
Scheme 11. Interconversion of Vinylidene Complexes 3CF3S03-and Acetylide Complexes ($-C,H,)Re(NO)(PPh,)(C=CR)
(6)
iil C
I
A
3 a,R=H b , R = CH, C , R = CeH, d , R = 1-CloH7
6
ac - 3
sc - 3
Ill
Ill
Ill
B ON ' F 4 PPh3
ON '
VI
VI11
B
HPPh3
VI1 Kinetic ratios (&& 3b (98 f 2):(2 k 2) 3c >99:1 3d >99:1
(Ua
Equilibrium ratios 3b (50f 2):(50f 2) 3c (20 2):(80f 2) 3d (20f 2):(80 2)
*
The Newman projection in the bottom part of Figure 2 illustrates the anti relationship of the C, naphthyl substituent and the PPh3 ligand in sc-3dPF6- (compare VII), thus confirming the Re=C=C geometric isomer assignments made above. The CB-CNp(C2-CI 1) bond defines 161.5" and 71.0" torsion angles with the Re-PI and Re-N bonds, respectively. Although the C, hydrogen was not located, its calculated position extends over the T cloud of the C61-4266 PPh3 phenyl ring. Distances to the phenyl carbons range from 3.24-3.29 8, (C61, C66) to 3.84-3.91 A (C63, C64). This accounts for the upfield ' H N M R shifts in sc Re= C=C isomers noted above. 4. Syntheses and Characterization of Acetylide Complexes (TJ~-C,H,)R~(NO)(PP~,)(C=CR) (6). Vinylidene complexes 3a-dCF3S03- were treated with bases K+-t-BuO- or TMP.27d Workup gave acetylide complexes 6a-d as powders in 53-93% yields (Scheme 11). Subsequent crystallization gave analytically pure 6b-d (72-82% from 3d-dCF3S03-). Acetylide complexes 6a-d were characterized by IR and 'H, I3C('H),and 3'P{1H)N M R spectroscopy (Table VI). In all cases, diagnostic weak IR uCIc were observed. The parent acetylide ~ cm-I. This complex 6a exhibited a sharp, medium IR Y ~ at - 3282 assignment was confirmed by the observation of an IR Y ~ at2268 cm-' in deuterioacetylide complex 6a-dl.28 A proton-coupled 13C N M R spectrum of 6a showed C, ( ' J C H = 228 Hz) to be downfield of C, (*JCH= 39.4 Hz). The C, carbon also showed an appreciable 'JcP, whereas ,JCp for C, was < I Hz. The downfield CEC resonances of 6b-d also showed ,JCpof < I Hz and were accordingly assigned to C,. Solutions of 6a-d were (28) Complex 6a-d, was prepared from deuterioacetyl complex 2a-d,, which was in turn synthesized from 1 and CD3MgLZ6
~
*
orange-red, and naphthyl acetylide complex 6d showed pronounced longer wavelength UV absorptions (Experimental Section) at 320 nm ( t 16000) and 360 nm (sh, t 7900). These bands were absent in 6b and naphthalene. 5. Reactions of Acetylide Complexes with Electrophiles. 1,3Asymmetric Induction. Reaction of methyl acetylide complex 6b and CF3S03H(1.0 equiv, CD2CI2)was monitored by ' H N M R at -78 "C. Methylvinylidene complex 3bCF3S03- rapidly formed as a (98 f 2):(2 i 2) mixture of ac/sc isomers (Scheme 11). Aryl acetylide complexes 6c-d were similarly treated with CF,SO,H. This gave arylvinylidene complexes nc-3c-dCF3S0,- as >99: 1 mixtures of ac/sc isomers. As a check, these solutions were kept at 25 "C for 24 h, and the equilibrium sc/ac isomer ratios noted above were obtained. These data are consistent with a transition state in which the protic electrophile approaches C, from a direction opposite to the bulky PPh, ligand. Such a transition state would give the less stable R e = C = C isomer when the electrophile is smaller than the acetylide complex C, substituent. Reaction of 6d with HPF6-Et20and room temperature workup gave the sample of sc-3dPF6- used in the above crystal structure. The reaction of methyl acetylide complex 6b and methylating agent CH3S03F(CD2CI2,-78 "C) was monitored by ' H NMR. Dimethylvinylidene complex [ (~s-C,Hs)Re(NO)(PPh3)(=C= C(CH3)2]+FS0,- (7bFS03-) formed cleanly at 0 "C (Scheme IIIa) and was isolated in 80% yield after recrystallization. Two 'H N M R methyl resonances were observed (6 1.96, 1.24; Table I). Similar reaction of 6b with the deuteriated methylating agent CD3S03F gave sc-[($-C,H,)Re(NO)(PPh,)(=C=C(CH,)(CD3))]+FS03-(sc-7b-d3FS03-; IX), in which the downfield 6 1.96 resonance of %BO3- was absent (detection limit 1%). Upon warming the sample above 0 "C, the 6 1.96 resonance appeared
6100 J . Am. Chem. Soc.. Vol. 110, No. 18, 1988
Senn et al.
Scheme 111. Stereospecific Methylation of Acetylide Complexes 6
CD3SO3F
1
ON’
”‘
‘PPh,
25°C
I + Re
Re
ON’
I +
Re
c -
!‘PPh,
ON’
!\PPh3
C
I
CH3
ac - 7b - d3F S O j
sc - 7b - d 3 F S O j
6b
8“
c3
Ill
Ill
CH3SO3F
c22
C23
c2 I +
c24
Re ON !’
\PPh3 D3C ON
H ON3 c &PPh3 X 3
CH, PPh3
M
Figure 3. Molecular structure of methyl acetylide complex ($-CsH5)Re( NO)( PPh,) (C=CCH3) (6b). Scheme IV. Reactions of Vinylidene Complexes with P(CH,),:
X
Stereochemistry of C, Attack 7b F S O j
Q
Kinetic ratio: >99:1 (ac/sc) Equilibrium ratio: 5050 (a/=)
P(CH,),
I +
Re ON’ CH3SO3F ON’
25°C
I +
Re
Re
‘PPh3
Ooc
ON’!\PPb
I +
6c
6
~
SC
ac - 7c F S O j
sc - 7~ FSOj
Ill
Ill
ON
PPh3
XI
‘PPh,
*fHR’
I CF3S03-
7bCF,SOi,
Re ON ;’
R = R’ = CH3
ac - 3b CF,SOi. R = H, R’ = CH,
I
I
*
(H3C),+P’
/\R
ICI \PPh3
C c
II
C ‘PPh,
!
Re ON’
Q
~
- 3b CF3SO3’, R = CH3, R’ = H
CF3S0,
8 CF,SOi, R = R’ = CH3 (Z)- 9 CF,SOi, R = H, R‘ = CH3 (E) - 9 CF,SOi, R = CH3, R’ = H
c ON 6 H s B C PPh3 H 3
XI1
Kinetic ratio: >99:1 (%/=) Equilibrium ratio: (25 f 2):(75f 2)
XI11
(wx)
6. X-ray Crystal Structure of Methyl Acetylide Complex
(q5-C5H5)Re(NO)(PPh3)(C----tCH3) (6b). We sought to deas the 6 .2+ resonance diminished. After 18 h at 25 OC, both resonances were of equal intensity. Thus, methylation of 6b occurred stereospecifically, and the stereochemistry was assigned (Scheme IIIa) by analogy to the above protonation reactions. Accordingly, the upfield methyl ‘H NMR resonance of 7bFS03(6 1.24) was assigned to the methyl group syn to the PPh3 ligand ( u c - C H ~ ~consistent ~~), with the C, proton shielding trends noted above. The reaction of phenyl acetylide complex 6c and CH3S03Fwas similarly monitored by ‘H NMR (Scheme IIIb). At 0 OC, methyl phenyl vinylidene complex ac- [(q5-C5H5)Re(NO)(PPh3)(=C= C(CH3)(C6H5))]+FS03-(ac-7cFS03-; XI) formed as a single Re=C=C isomer, the stereochemistry of which was assigned by analogy to the above reactions. Complex ac-7cFSO< equilibrated to a (75 f 2):(25 f 2) sc/ac mixture over the course of 4 h at 30-45 “C. Hence, as with the protonation of 6c, the less stable Re=C=C isomer formed initially. As expected, the ‘H N M R methyl resonance of the sc isomer (XII; 6 1.58) was upfield of that of the ac isomer (XI; 6 2.33).
termine whether a distortion of the ideally linear Re-C,=,-R linkage in acetylide complexes 6a-d might contribute to the stereospecificityof C, electrophilic attack. Hence, X-ray data were collected for methyl acetylide complex 6b as summarized in Table 11. Refinement, described in the Experimental Section, yielded the structure shown in Figure 3. The near-linearity of the Re-C,=C, (Re-Cl-C2) and C,=C,-C, (Cl-C2-C3) linkages (1 76-1 77O) is evident. Positional parameters, bond distances, and bond angles are summarized in Tables VII-IX. 7. Rates of Interconversion of Vinylidene Complex Re=C==C Isomers. The rates of Re=C=C isomerization of vinylidene complexes ac-3b-dCF3S03-were measured as outlined in Table X. The ac a sc Kq:which were needed to extract kl from koW, did not change significantly over the temperature range of the rate measurements. The kl values gave the activation parameters summarized in Table X. Control experiments were conducted to probe whether Re= C-C isomerization might occur by a C, deprotonation/protonation mechanism. First, similar isomerization rates and acti-
J. Am. Chem. Soc., Vol. 110, No. 18, 1988 6101
Rhenium Acetylide and Vinylidene Complexes
P
(a)
H P
lt*
(b)
Figure 4. Comparison of vacant acceptor orbitals in (a) alkylidene and (b) vinylidene ligands.
vation parameters were obtained for methyl phenyl vinylidene complex ac-7cFSOq (Table X), which lacks a C, proton. Second, the concentration of the CF,SO< counteranion, the most plausible proton carrier, was varied. The isomerization rate of ac3dCF3S03- was measured in the presence of added (nC4H9)4N+CF,S03-(0.27 equiv). This gave k , = 6.20 X lo4 s-' (25.4 "C), slightly lower than that without added triflate (6.75 X lo4 s-l, 24.6 OC). Tetrafluoroborate complexes ac-3cBF4- and ac-3dBFI were generated from HBF4.Et20and the corresponding acetylide complexes at -78 "C. Their isomerization rates ( k , = s-, (25.4 "C)) were s-l (22.2 "C) and 5.27 X 6.27 X comparable to those in Table X. Hence, it is concluded that Re=C=C isomerization occurs predominantly or exclusively by simple bond rotation. The IH N M R spectra of parent vinylidene complex 3aCF,SO
