Abstract:RECENT crystallographic studies have shown that in some phenylphosphine complexes of transition metals there is interaction between an orthohydrogen of the phenyl ring and the metal atom.192 This observation has led us to study metal complexes of trispentafluorophenylphosphine, since the 19F n.m.r. spectra of these compounds might indicate if there is a similar interaction between the ortho-fluorines and the metal.
“…26 Hz). This explanation did not seem implausible given the ample evidence for restricted rotation about M-C 6 F 5 bonds [40][41][42][43][44][45][46][47][48][49] and for slowed rotation about M-P and P-C bonds in platinum(II) complexes of (C 6 F 5 ) 3 P. [50][51][52] However, the frequency separation between the pairs of doublets was found to be the same at 202.3 MHz as at 121.4 MHz; hence there is only one 31 P chemical shift and the observed pattern can only be due to P-F coupling.…”
Reaction of 2-LiC6F4PPh2 with [MCl2(SEt2)2] in diethyl ether gives the monomeric bis(chelate) complexes trans-[M(κ2-2-C6F4PPh2)2] [M = Pt (1), Pd (2)] or, in the case of platinum, a mixture of cis- and trans-isomers. Treatment of a mixture of NiCl2 and 2-BrC6F4PPh2 in THF with zinc dust gives trans-[Ni(κ2-2-C6F4PPh2)2] (3). The four-membered chelate rings in 1−3 are opened on addition of the bidentate ligand 1,2-bis(diphenylphosphino)ethane (dppe), and, in the case of 3, 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen), to give complexes of the type cis-[M(κC-C6F4-2-PPh2)2(L-L)] [L-L = dppe, M = Ni (6), Pd (7), Pt (8); M = Ni, L-L = bipy (9), phen (10)], in which the PPh2 groups are uncoordinated. Complexes 6−8 show unexpectedly large four-bond coupling constants (4
J
PF), in the range 75−95 Hz, between the fluorine atoms (F6) ortho to the metal−carbon σ-bond and the phosphorus atoms of the PPh2 groups, possibly because F6 and the lone pairs on phosphorus adopt a close to synperiplanar conformation. Treatment of 2 with [PdCl2(NCMe)2] gives the dinuclear complex [Pd2(μ-Cl)2(κ2-2-C6F4PPh2)2] (11), which dimerizes in solution to the tetranuclear complex [Pd4(μ-Cl)4(μ-2-C6F4PPh2)4] (12) as a result of opening of the chelate 2-C6F4PPh2 rings. Carbon monoxide inserts into a nickel−carbon σ-bond of 3 to give, after oxidation, bis-2,2′-(diphenylphosphinoyl)octafluorobenzophenone, {2,2′-C6F4P(O)Ph2}2CO (14). The molecular structures of complexes 1−3, 6, 8, 9, and 14 have been determined by single-crystal X-ray methods.
“…26 Hz). This explanation did not seem implausible given the ample evidence for restricted rotation about M-C 6 F 5 bonds [40][41][42][43][44][45][46][47][48][49] and for slowed rotation about M-P and P-C bonds in platinum(II) complexes of (C 6 F 5 ) 3 P. [50][51][52] However, the frequency separation between the pairs of doublets was found to be the same at 202.3 MHz as at 121.4 MHz; hence there is only one 31 P chemical shift and the observed pattern can only be due to P-F coupling.…”
Reaction of 2-LiC6F4PPh2 with [MCl2(SEt2)2] in diethyl ether gives the monomeric bis(chelate) complexes trans-[M(κ2-2-C6F4PPh2)2] [M = Pt (1), Pd (2)] or, in the case of platinum, a mixture of cis- and trans-isomers. Treatment of a mixture of NiCl2 and 2-BrC6F4PPh2 in THF with zinc dust gives trans-[Ni(κ2-2-C6F4PPh2)2] (3). The four-membered chelate rings in 1−3 are opened on addition of the bidentate ligand 1,2-bis(diphenylphosphino)ethane (dppe), and, in the case of 3, 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen), to give complexes of the type cis-[M(κC-C6F4-2-PPh2)2(L-L)] [L-L = dppe, M = Ni (6), Pd (7), Pt (8); M = Ni, L-L = bipy (9), phen (10)], in which the PPh2 groups are uncoordinated. Complexes 6−8 show unexpectedly large four-bond coupling constants (4
J
PF), in the range 75−95 Hz, between the fluorine atoms (F6) ortho to the metal−carbon σ-bond and the phosphorus atoms of the PPh2 groups, possibly because F6 and the lone pairs on phosphorus adopt a close to synperiplanar conformation. Treatment of 2 with [PdCl2(NCMe)2] gives the dinuclear complex [Pd2(μ-Cl)2(κ2-2-C6F4PPh2)2] (11), which dimerizes in solution to the tetranuclear complex [Pd4(μ-Cl)4(μ-2-C6F4PPh2)4] (12) as a result of opening of the chelate 2-C6F4PPh2 rings. Carbon monoxide inserts into a nickel−carbon σ-bond of 3 to give, after oxidation, bis-2,2′-(diphenylphosphinoyl)octafluorobenzophenone, {2,2′-C6F4P(O)Ph2}2CO (14). The molecular structures of complexes 1−3, 6, 8, 9, and 14 have been determined by single-crystal X-ray methods.
“…The observed inequivalence of all the olefinic protons of COD presumably arises from restricted rotation about the Pt–C(aryl) bond. There are numerous examples of restricted rotation about the metal–carbon bonds in Pt–C 6 F 5 complexes, − and there is evidence for slowed rotation about M–P and M–C bonds in complexes of (C 6 F 5 ) 3 P. − …”
The reaction of [PtI 2 (1,5-COD)] with 2-LiC 6 F 4 AsPh 2 affords the planar platinum(II) fluoroaryl complex [PtI(κC-2-C 6 F 4 AsPh 2 )(1,5-COD)] (7), in which the arsenic atom is not coordinated to the metal atom. Attempts to prepare the bis(chelate) complex [Pt(κ 2 As,C-2-C 6 F 4 AsPh 2 ) 2 ] analogous to the known phosphorus compound failed. Removal of iodide ion from 7 with TlPF 6 gave [Pt(κ 2 As,C-2-C 6 F 4 AsPh 2 )(1,5-COD)]PF 6 (8), in which 2-C 6 F 4 AsPh 2 is now coordinated as a bidentate ligand, giving a four-membered chelate ring. Alternatively, protonolysis (with triflic acid) of the methyl complex [PtMe(κC-2-C 6 F 4 AsPh 2 )(1,5-COD)] (15), which is obtained from 7 and dimethylzinc, gives the triflate salt 16 of the same chelate cation. The chelate As,C ring in 8 is readily reopened when the complex is treated with pyridine or with halide ions, forming respectively [Pt(py)(κC-2-C 6 F 4 AsPh 2 )(1,5-COD)]PF 6 (9) and [PtX(κC-2-C 6 F 4 AsPh 2 ](1,5-COD)] (X = Cl (10), Br (11), I (7)). The appearance of two pairs of olefinic COD resonances in the proton NMR spectra of 7, 10, 11, and 15 may indicate that there is restricted rotation about the Pt−κC-2-C 6 F 4 AsPh 2 bond; the additional signals are not evident in the spectra of 8 or 16. Complexes 7 and 10 form the 1:1 adducts [PtX(μ-2-C 6 F 4 AsPh 2 )(1,5-COD)AuY] (X = Cl, Y = I (12); X = Y = I (13); X = Y = Cl (14)) by attachment of gold(I) halides to their dangling arsenic atoms. In 12 the halides are scrambled between platinum and gold. The X-ray structures of 7, 8, 9, 12, 15, and 16 are reported, and possible reasons for the poorer chelating ability of 2-C 6 F 4 AsPh 2 in comparison with that of 2-C 6 H 4 PPh 2 are discussed.
“…Furthermore, the synthetic strategy we have developed for complexes of these ligands (Scheme 3) necessitates a strongly electron-withdrawing polyfluoroaryl phosphine substituent, which reduces the basicity and increases the cone angle of the phosphine compared to the nonfluorinated analogue. On the basis of past observations both of these effects are expected to increase the lability of the phosphine moiety. …”
The pentafluorophenyl-substituted diphosphine (C6F5)PhPCH2CH2PPh(C6F5) has been prepared, as a
1:1.7 mixture of rac (1a) and meso (1b) isomers, in four steps from dppe. The reaction between [Cp*RhCl(μ-Cl)]2 and 1 in the presence of tetrafluoroborate yielded a mixture of racemic diastereoisomers of
[Cp*RhCl(κP,κP-1a)][BF4] (4a·BF
4
) and trans and cis isomers of [Cp*RhCl(κP,κP-1b)][BF4] (4b·BF
4
and 4c·BF
4
, respectively). On addition of Proton Sponge, 4a and 4c, in which at least one pentafluorophenyl
group is close to the pentamethylcyclopentadienyl ligand, underwent rapid dehydrofluorinative carbon−carbon coupling giving trans- and cis-[{η5,κP,κP-C5Me4CH2C6F4-2-PPhCH2CH2PPh(C6F5)}RhCl]+ (5
and 6), respectively. The latter underwent further dehydrofluorinative carbon−carbon coupling to give
two isomers of [{η5,κP,κP-C5Me3[CH2C6F4-2-PPhCH2]2}RhCl]+ (7). Isomerization of 4b to 4c was
observed in chloroform and dimethlysulfoxide. Neither isomerization of 4a to 4b or 4c nor isomerization
of 5 to 6 was observed at ambient or elevated temperature in dimethyl sulfoxide. The results provide the
first evidence that complexes of η5,κP,κL-cyclopentadienyl-phosphine-donor ligands are configurationally
stable at high temperature.
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