David G . Cooper and John Powell
142 Inorganic Chemistry, Vol. 16, No. 1, 1977 R F C O group ~ trans to triphenylphosphine should be the most labile, it may be preferentially lost as free acid. This eventuality can be accommodated by a mechanism essentially similar to that given in Scheme I1 and does not invalidate this discussion. We are unable to ascertain whether the step c-d involves simultaneous or sequential carboxylic acid loss and hydride migration. If the latter situation prevails then the following complexes could be intermediates in the reaction cycle OCH,R
L
OCHzR
L
(35) T. G. Appleton, H. C. Clark, and L. E. Manzer, Coord. Chem. Reo., 10, 335 (1973). (36) A. J. Deeming and B. L. Shaw, J . Chem. Soc. A , 1128 (1969). (37) M. S. Lupin and B. L. Shaw, J . Chem. Soc. A , 741 (1968). (38) A . C. Skapski and F. A. Stephens, J . Chem. Soc., Dalton Trans., 390 (1974). (39) i:S. Kolomnikov, A. I. Gusev, G. C. Aleksandrov, T. S. Lobeeva, Yu. T. Struchkov, and M. E. Vol'pin, J . Orgunomet. Chem., 59,349 (1973). M. J. Bennett, K. G. Caulton, and F. A. Cotton, Inorg. Chem., 8, 1 (1969). F. A. Cotton and J. G. Norman, Inorg. Chim. Acta, 6, 41 1 (1972). P. B. Critchlow and S. D. Robinson, J . Organomer. Chem., 114, C46 (1976). (43) Typical data from ref 3841: Ru-OCOMe = 2.21-2.22 8, (trans to PPh3) and 1.96-2.09 8, (trans to OCOMe); Ru-PPh3 = 2.35-2.37 8, (trans to PPh3) and 2.23-2.28 8, (trans to OCOMe).
Contribution from the Lash Miller Chemical Laboratories, University of Toronto, Toronto, Ontario, Canada M 5 S 1 A l
13C Nuclear Magnetic Resonance Studies of Organoplatinum(I1) Complexes Containing Substituted Pyridine Ligands DAVID G . C O O P E R and J O H N P O W E L L * Receiced May 12, 1976
AIC60348C
13CN M R data are reported for the series of platinum(I1) compounds trans-[LPtC12(NC5H4-4X)] (L = ethylene, styrene, di-tert-butylacetylene, or carbon monoxide; NCsH4-4X = a series of para-substituted pyridines), trans-[ZPt(NCSHd4X)(PMezPh)z]BF4 ( Z = CH3, CH3C-Q and [C1(2-methoxy-5-cyclooctenyl)Pt(NC~H4-4X)]. These complexes provide examples of olefins, acetylenes, carbonyls, alkyls and acetylides bonded to platinum(I1) in trans position to a para-substituted pyridine. Small changes in the 6C and I J 1 9 s p t - q data of the directly bound carbon atoms as X is varied have been interpreted in terms of slight fluctuations in the u-donor component of these platinum-carbon bonds (regardless of ligand type). The spectra of the 2-methoxy-5-cyclooctenyl complexes also demonstrate the presence of two geometrical isomers in solution contrary to previous reports
Introduction A large amount of data have been published recently regarding the I3C N M R spectra of organometallic compounds of the transition element~.l-*~ Interpretation of the reported chemical shifts is difficult because several parameters determine these values. In fact, a recent, short overview of the subject25concluded that it was not possible to satisfactorily explain the chemical shifts of directly bound carbon nuclei attached to transition metals using current theories. A study of trends in I3C N M R data obtained from series of closely related compound^^^^^^^^^ should lead to more meaningful rationalizations. However even this approach has been only partially successful because changing only one ligand on the metal still has both an electronic and a steric effect, and in many cases, even the mode of bonding is altered. In an attempt to circumvent these problems, we have considered series of organometallic complexes with parasubstituted pyridines N C 5 H 4 - X as ligands. As these para substituents are varied, there should be no change in the steric parameters of the pyridine ligands near the metal, such that the mode of the bonding between the metal and the nitrogen should remain essentially unchanged. Thus, the only change experienced by the metal (and the trans metal-carbon bond) when the para substituent is varied will be electronic in origin. This work considers the I3C N M R data obtained for the series of platinum(I1) complexes 1-4. Platinum is an ideal metal for I3C N M R studies because: (i) 195Pt(33% natural abundance) couples strongly with directly bonded carbon nuclei, and (ii) it is possible to synthesize a large variety of stable platinum-carbon bonds. The series of compounds 1-4 provide examples of acetylene, olefin, carbon monoxide, methyl, and acetylide groups bound to platinum(I1) in the trans position to N C 5 H 4 - X . Experimental Section et
Complexes of type 1 were prepared using the methods of Orchin Compounds of type 22,3s32and the dimer 333were prepared
CI
1 CI
4
1 , L=H,C'=CH,,
5
,
H,C 1 --C 2H -6 k=d
(C3",),C2C'SC(CH3),,
C'=O
P I P
BF;
2, P = P M e , P h ; Z = C 1 H , , C 1 ~ C 2 ~ C 3 H , CMe
3
CMe
CMe
4a
4b
X = NMe,, 0 - n - B u , Me, H, C1, CO,Me, COMe, CN by standard methods. The complexes 4a and 4b were not isolated from solution; however, several of them have been ~ h a r a c t e r i z e d . ~ ~ The I3CN M R spectra were measured at ca. 35 "C on either Varian XL-100-15 or CFT-20 spectrometers operating in the Fourier transform mode at 25.2 and 20.0 M H z , respectively. All the spectra (except 1, L = CO) were determined with noise modulated proton decoupling.
Results Data for complexes of type 1 are recorded in Table I.35 Only spectral data where 3 J p t - ~coupling to the 0carbons of the pyridines is observed (ca. 35-40 Hz) are completely reliable. The complexes were recrystallized several times to remove excess pyridine which, if present, can catalyze the
13C N M R Studies of Organoplatinum(I1) Complexes
Inorganic Chemistry, Vol. 16, No. I , 1977 143
Table I. 13C NMR Data3' for the Complexes 1 of the Type trans-[(p-X€,H,N)Pt(CI),(L)]in CDCI, Solutions@
L = ethylene
L = (C3H3),C2C1=€C(CH3),
L = C'O
X
6
1J195ptJ3c
6C'
1Jpt-cl
6C2
'Jpt-CZ
6C3
N(CH ,) O(CF2),CH,b CH, Hb Clb CO,CH, COCH, CN
73.35 74.18 75.05 75.23 75.12 75.66 75.83 75.95
162.5 165.4 164.4 167.9 168.8 (166.7)' (166.3)' (168.9)'
76.18
182.2
29.27
15.3
30.75
76.34 76.40
183.4 183.5
29.38 29.58
16.7 15.7
30.70 30.75
co
' JPt-C'
15 1.86 151.33 151.10
1649.5 1656.6 1669.7
150.53 149.70
1692.2 1726.0
6
L = styrene Aromatic carbons
Olefinic carbons 6C' N(CH ,1 O(CF2),CH,b CH 3 Hb Clb COCH CN
'JPt-C] 163.9 166.4 165.8 167.2 169.5 (168.2)' (170.0)'
61.65 61.72 62.09 62.11 61.84 62.28 61.97
6C2 95.37 96.72 97.59 98.19 98.32 99.12 100.04
' JPt-C '
6C3
'Jpt-c,
6C4
'Jpt-c4
6C5
SC6
138.3 138.4 137.6 139.9 140.9 (135.3)' (132.6)'
136.03 135.67 135.49 135.44 135.28 135.24 135.07
36.2 35.0 36.2 36.4 37
129.87 129.68 129.92 129.92 129.92 130.02 130.09
13.4 12 12.8 12.4 12.6
128.30 128.37 128.37 128.40 128.46 128.47 128.59
129.56 129.68 129.92 130.06 130.19 130.25 130.52
a 6 in ppm relative internal Me,%, J's in Hz. The p carbon of the pyridine has I9'Pt satellites for these compounds: 3Jpt-13~p= 35-40 Hz. ' These are the largest values obtained (in the presence of [PtCL,(C,H,)],) b u t they are not reliable because of fast exchange of the trans pyridines (see text). They should be regarded as minimum values.
Table 11. I3C NMR Data3' for Complexes of the Type ~~U~~-[(~-X€,H,N)P~(M~,P~P),(Z)]~BF~in CDCl,=
Z =C1H3b
'
Z = C'+z-C3H,b
X
SC'
IJPt-CI
6C1
'JPt-C'
6C'
'JPt-C2
6C3
N(CH 3 12 O(CH,),CH, CH 3 H C(O)CH3 CN
-23.60
5 89.4
60.90 59.66
1225.0 1238
100.55 100.46
355.4 359.1
5.50 5.60
-23.0f -22. 7f3g
594f 598f,g
58.88 58.44
1251.2
100.77 100.58
362.2
5.66 5.51
-22.80
e
e
27 27
599.9
' 'JJP-C' = 6.3 Hz
J's in Hz. Coupling between 195Ptand the pyridine p carbons ca. 30 Hz. "Jp-cz ca. 2.5 Hz. Data from ref 2. g Solvent acetoneil,.
a 6 in ppm relative to internal Me,Si,
,Jp-c' ca. 16 Hz.
3JPt-C3
exchange of the coordinated ~ y r i d i n e . ~The ~ , most ~ ~ noticeable effects as the free + coordinated pyridine exchange rate increases are (i) the loss of lg5Pt coupling to the pyridine carbons and (ii) a small decrease (
