195Pt NMR spectra of ferrocenylketimine complexes of platinum(II)

Polyhedron Vol. 17, No. 10, pp. 1725 1728, 1998

~

Pergamon PII: S0277-5387(97)00442-7

(C 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0277 5387/98 $19.00+0.00

19spt NMR spectra of ferrocenylketimine

complexes of platinum(II) Li Ding, Yang Jie Wu* and Da Peng Zhou Department of Chemistry, Zhengzhou University, Zhengzhou 450052, P.R. China

(Received 25 August 1997; accepted 27 October 1997)

Abstract--The ~95pt N M R spectra of two series of 18 ferrocenylketimine complexes of platinum(lI) which include 9 cycloplatinated derivatives [a-Pt{(qs-CsH3CMe=NAr)Fe(qS-CsHs)}(DMSO)C1 ] (1) and 9 coordinated compounds [trans-PtC12(DMSO){(qs-CsH4CMe-=NAr)}Fe(q%CsHs)] (2) (Ar = substituted phenyl groups) have been recorded. The ~95ptchemical shifts are regularly affected by the substituents in the N-phenyl rings, and satisfactory to excellent linear relationships are found to exist between the ~95pt shifts (6) and Hammett substituent constants in both series. The directions of the substituent effect on 6(~95pt) are the same in both series, i.e., electron-donating substituents cause shifts to higher frequency, and the coordinated compounds have a better linear relationship. These wsPt N M R features support the existence ofintramolecular coordination between the imino nitrogen atom and the platinum(II) and n-~ conjugation between the nitrogen and the N-phenyl ring. © 1998 Elsevier Science Ltd. All rights reserved Keywords: ~95pt N M R spectra; ferrocenylketimine complexes of platinum(II); substituent effect; intramolecular coordination.

The chemistry of platinum spans a gap which includes heterogeneous catalysts for automobiles [1], homogeneous catalysts for organic synthesis [2], and cancer drugs [3]. Consequently an increasing number of chemists express an interest in t95Pt nuclear magnetic resonance and the number of reports containing ~95pt data on organometallic complexes has steadily increased. To the best of our knowledge, so far none of the ~95pt N M R studies has described the linear correlations between I95pt shifts (6) and Hammett substituent constants (ap or am). There are only two reports of ~95pt N M R involving ferrocenyl platinum complexes [4]. Herein we report the ~95pt chemical shift in solution and the linear correlations between 6(195pt) values and Hammett substituent constants ap or a,, for the following ferrocenylketimine derivatives of platinum(II).

procedure [5], based on the reaction of the free ligands with stoichiometric amounts of cis-Pt(DMSO)2CI2 in refluxing toluene. The J95pt chemical shifts for compounds ! and 2 are listed in Table 1.

NAr

©'

Ck,,x

~

RESULTS AND DISCUSSION

~95pt NMR spectra

Fe

The ferrocenylketimine complexes of platinum(II) ! and 2 were synthesized according to the published

© 2

* Author Io whom correspondence should be addressed. 1725

DMSO

CH3

P t Ar

/

DMSO CI

L. Ding et al.

1726

Table l.~95Pt NMR chemicalshi~s6 ~rcompoundsl and 2

Compounds

6L (ppm)

Compounds

62 (ppm)

la lb lc ld le If lg lh li

- 3790.1 -3797.7 - 3802.7 - 3804.6 - 3805.0 - 3819.7 - 3800.7 - 3808.3 - 3815.0

2a 2b 2c 2d 2e 2f 2g 2h 2i

-2966.1 -2966.9 -2968.8 -2975.9 -2976.1 -2988.2 -2967.9 -2978.0 - 2985.3

among its valence orbitals, and will result in a change in a p [7]. As shown in Table 1, the ~95pt shifts show obvious dependence on the nature of the substituents in the N-phenyl ring, with lower frequency shifts resulting from electron-withdrawing groups and with higher frequency shifts resulting from electron-donating groups. Such a trend has also been found in the 199HgN M R spectra of ferrocenylimine derivatives of mercury [8]. Satisfactory to excellent linear correlations between 195pt shifts (6) and Hammett substituent constant at, or or,, [9] were obtained for both series (Eqns (1) and (2) for compounds 1 and 2, respectively). 6~ = - 3 8 0 0 . 2 - 2 3 . 3 a

n= 9

r = -0.975

(1)

62 = - 2 9 7 0 . 5 - 2 1 . 7 a

n=9

r=-0.991

(2)

For the trans derivatives 2, the 195pt chemical shift falls within the range of -2966.1 to -2988.2 ppm, characteristic of a PtNSX2 donor set. An analogue is trans-PtC12(NH3)(DMSO) for which 6(~gspt) is - 3 0 6 7 ppm [6]. A PtNOX2 donor set is expected to give values in the range of - 1600 to - 1800 ppm [4a]. The results obtained confirm that the DMSO is Sbound in solution. Cycloplatination results in a large lower frequency shift to a range of -3790.1 to - 3 8 1 9 . 7 ppm, making easy identification of this type of product. A closely comparable shift in the literature [4a] was - 3 8 9 9 ppm for compound [cr-Pt{(q5CsH3CH (Me)NMe2) Fe(r/5-fsHs) }(DMSO)C1]. It is usually convenient to discuss the magnetic shielding of the heavier nuclei principally in terms of local "paramagnetic" and "diamagnetic" contributions a p and a a. Metal chemical shifts are dominated by changes in the paramagnetic screening contribution, a p, to the total shielding [6a]. This term depends upon (a) the asymmetry of the electronic distribution within the valence 5d and 6p orbitals of the platinum atom, (b) the mean inverse cube of the distance between these electrons and the platinum nucleus, and (c) the inverse of the energy separations between the ground and excited states for these electrons. A decrease in halide content normally causes a ~95pt shift to lower frequency on the basis of electronegativity differences and changes in electronic asymmetry [6b], so the lower frequency shift of cycloplatination is a direct consequence of a - P t - - C bond formation. The higher frequency shift of compounds 2 may be tentatively ascribed to a strong trans effect, which makes a difference in crP due to the change in electronic excitation energy. This phenomenon is in accordance with that noted elsewhere [6b]: for [PtC12(PR3)2] and [PtC12(AsR3)2] types, the shift of the cis complex is at lower frequency than that of its trans analogue by 400-500 ppm.

However, no obvious correlation with substituent effect has been found for the meta- and para-substituted arylplatinum cyclooctadiene compounds [7]. It is noteworthy that the ~95pt chemical shifts of compounds 2 are less sensitive to the change of the substituents in the N-phenyl ring in comparison with compounds 1 (see slope in Eqn (1) which is larger than that in Eqn (2)). The X-ray crystal structures [5] (Fig. 1) have shown that P t - - N bond length of compound 2e is shorter than that of compound lc, and the angle between the N-phenyl ring and the plane of C - - C ~ N - - C in 2c is larger than that in le (68.24 ° and 87.43 ° for le and 2e, respectively). If only nn conjugation involving the n-electrons of the imino nitrogen and n-electrons of the N-phenyl group is considered, the substituents in the N-phenyl ring should have a much stronger effect on platinum for compounds 2 than that for compounds 1. A possible explanation is that the substituents affect the platinum of compounds 1 not only by means of the N ~ Pt interaction, but also via part transmission of electronic effects through the C = N bond and the substituted Cp ring, though the nonplanarity of the Nphenyl ring and the plane C--C~---N--C destroys the n-n conjugation between the C = N bond and the Nphenyl group to some extent. As for compounds 2, there is only N --* Pt interaction. It is believed that there is an interaction between the n-electrons and unoccupied 5d and 6p orbital of the platinum atom [10]. In this way, the electrondonating groups should enhance the unbalance of electron distribution in the unoccupied orbital of the platinum, thus leading to an increase in the paramagnetic shielding term a p with observed higher frequency shift while the electron-withdrawing groups have an opposite effect.

Effects o f substituents o f N-phenyl riny

The details for the synthesis and characterization of compounds 1 and 2 have been described previously [5]. J95pt NMR spectra were recorded on a Bruker

Electronic withdrawal by a substituent connected to the platinum atom modifies the electronic unbalance

EXPERIMENTAL

195pt N M R spectra of ferrocenylketimine complexes of Pt(II) C14

1727

CI5

C'/ C'3 C6

CII C12

S~YMU~Cl9

CI

N - - P t 2.095(5) A Angles( ° ) between planes: A and B 68.24, A and C 62.35.

lc:

C9

CI9

Cll d CI0

(212 CI ~Cll

N 02

I~

C2U i

2c:

N--Pt

2.049(4) A

Angles( ° ) between planes: A and B 87.43, A and C 90.94.

c~

C15 Fig. 1. The structures and some parameters of the ferrocenylketiminecomplexes of platinum(II) with A, B and C representing the N--Ar ring, plane of C(Cp ring)--C=N and substituted Cp ring, respectively.

DPX-400 spectrometer in CDCI 3 at 20°C with Na2PtCI6 in D20 as an external standard. The operating frequency was 86.0 MHz and the routine acquisition parameters used were as follows: pulse width, 12.00 #s, acquisition time 0.64 s, spectral width 51,546.39 Hz.

4.

Acknowledgements--We are grateful to the National Natural Science Foundation of China (Project 29592066) and the Natural Science Foundation of Henan Province for financial support to this work.

5.

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