Reactions of cationic isocyanide platinum(II) complexes with water (from hexafluoroacetone-hydrate): Carboxamido and isocyanato complexes

Article abstract of DOI:10.1002/zaac.200700540

The isocyanide complexes [Pt(Cl)(C≡NR)(PPh₃) ₂]⁺BF₄ (R = CH₂CO₂Et, CH₂Ph, C₆H₁₁, CH₂SO ₂C₆H₄-p-Me) react with he

Full text of DOI:10.1002/zaac.200700540

DOI: 10.1002/zaac.200700540
Reactions of Cationic Isocyanide Platinum(II) Complexes with Water (from
Hexafluoroacetone-hydrate): Carboxamido and Isocyanato Complexes
Wolf Peter Fehlhammer*, Klaus Bartel, Robert Metzner, and Wolfgang Beck
München, Department Chemie und Biochemie der Ludwig-Maximilians-Universität
Received December 4th, 2007.
In memory of Professor Helmut Behrens
Abstract. The isocyanide complexes [Pt(Cl)(CϵNR)(PPh3)2]ϩBFϪ4
(R ϭ CH2CO2Et, CH2Ph, C6H11, CH2SO2C6H4-p-Me) react with
hexafluoroacetone-sesquihydrate, (F3C)2CO·1,5 H2O, in the presence
of triethylamine to give the carboxamido (carbamoyl) complexes
[Pt(Cl){C(ϭO)NHR}(PPh3)2]. Under the same conditions the iso-
cyanoamine complexes trans-[Pt(Cl)(CϵN-NR2)(PPh3)2]ϩBFϪ4
(R ϭ Et, Pri, 2R ϭ C
TH(Me)(CH2)3CUH(Me)) are transformed into
the isocyanato complex trans-[Pt(Cl)(NCO)(PPh3)2].
Keywords: Platinum; Isocyanides; Carboxamido complexes; Iso-
cyanato complexes
Introduction
The addition of nucleophiles Y-H (Y ϭ NHR, OR, SR)
to coordinated isocyanides, first described by Chatt et al.,
provides a rational and often applied route to (bis-hetero-
atom-stabilized) aminocarbene complexes [12, 13]. Even
earlier Saegusa et al. had discovered that ͰϪadditions of
the same H-active nucleophiles to isocyanides yielding
Y-CHϭNR are catalyzed by group 11 and 12 metals in
various oxidation states [14], and it was primarily Bonati
and his group who isolated carbene complexes of these
metals thus proving their intermediacy in the catalytic pro-
cess [13].
From their discovery to this day carboxamido (carbamoyl)
complexes [LnM-C(ϭO)NHR] have enjoyed great interest
of many research groups. Particularly successful studies
have been carried out by King [2], Angelici [3], and Behrens
[4] and their coworkers. Various synthetic routes to this
kind of complexes have been described
Ϫ the addition of amines or ammonia to coordinated CO
ligands [3, 4] and the related reaction of PdII complexes
with free CO and amine [3, 5, 6],
Chatt’s synthetic access to carbene complexes has been
followed in our groups and extended to include CH-acidic
nucleophiles (e.g. CH(CN)2Ϫ) as well as functional isocyan-
ides carrying nucleophilic reagents in their side chain
[15Ϫ18]. In the course of our studies on the chemistry of
isocyanide metal complexes we became interested in a
method which allows the removal of this ligand under mild
conditions. An attractive possibility appeared to us its con-
version with OHϪ/H2O into a carboxamido species which
is known to be easily cleaved on protonation yielding a CO
ligand and free amine (ammonium) [3] (eq. (1)).
Ϫ the oxidative addition of carbamoyl chlorides
R2NC(O)Cl to low valent or anionic metal complexes
[2, 3, 5],
Ϫ the insertion of organic isocyanates into a metal-hydride
bond [3, 7],
Ϫ the insertion of CO into the rhenium-nitrogen bond of
an organometallic imide complex [8],
Ϫ the addition of hydroxide to the dicationic isocyanide
complex [Pt(CNMe)2(PPh3)2]2ϩ [9],
Ϫ the cycloaddition of arylnitrile oxides to the metal-isocy-
anide in [CoCp(CNR)(PMe3)] [10],
OHϪ
Hϩ
Ǟ [LnM-C(ϭO)NHR]Ϫ
[LnM-CO] ϩ RNH3
Ǟ
(1)
Ϫ the [3ϩ2] cycloaddition between the platinio nitrile ylid
[Pt(Cl)(CϵN-CH-CO2Et)(PPh3)2] and salicylic aldehyde
and consecutive reactions [11].
[LnM-CNR]
ϩ
Treichel [9] had reported on the reaction of [Pt(CNMe)2-
(PPh3)2]2ϩ with OHϪ which afforded the carboxamido com-
plex [Pt{C(ϭO)NHMe}(CNMe)(PPh3)2]ϩ. In our hands, how-
ever, the action of hydroxide (KOH/MeCN, NaOH/H2O/
CH2Cl2/(NEt4)Cl) on neutral ([PtCl2(CNR)(PPh3)]) or mono-
cationic platinum complexes ([PtCl(CNR)(PPh3)2]ϩ) did
not lead to well-characterized products though the isocyan-
ide ligands had disappeared (IR) during the reaction
Prof. Dr. Dr. h.c. Wolf Peter Fehlhammer
Department Chemie und Biochemie
Universität München
Butenandtstr. 5Ϫ13
D-81377 München
E-mail: wpfehlhammer@gmx.de
1002
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 634, 1002Ϫ1004

Reactions of Cationic Isocyanide Platinum(II) Complexes with Water
“OHϪ”
[18, 19]. Presumably, any carbamoyl complexes that might
have been formed are too labile in the presence of excess
hydroxide. With the versatile reagent hexafluoroacetone-hy-
drate [20] we found a reagent which supplies only the stoi-
chiometric amount of hydroxide necessary for the forma-
tion of the carboxamido from the isocyanide ligand.
trans-[Pt(Cl)(CϵN-NR2)(PPh3)2]ϩ
Ǟ
<[Pt(Cl){C(ϭO)-NH-NR2}(PPh3)2]>
Ǟ
-HNR2
(3)
trans-[Pt(Cl)(NϭCϭO)(PPh3)2]
5
In this context it may be interesting to note that pre-
viously we succeeded in the transformation of carbamoyl
back to isocyanide complexes by using the reagent phos-
gene/triethylamine for the elimination of hydroxide [21].
This result is in perfect agreement with a related work by
Angelici [25] who on addition of hydrazine or its mono- and
N,N-dialkylated derivatives to the CO ligand also observed
the formation of isocyanate with elimination of ammonia
or amine, respectively. A similar mechanistic sequence
Ϫ nucleophilic addition to the metal-bonded carbon atom
of N-isocyanide complexes, cleavage of the N-N bond and
C Ǟ N migration of the metal atom Ϫ is obviously at work
in the reactions of [M(CO)5CϵN-NR2] (M: Cr, W) with
secondary amines (HNRЈ2) which (unlike primary amines
[17]) give the corresponding cyanamide complexes
[M(CO)5NϭCϭNRЈ2] [26]. Further reference is made to
the analogies with the chemistry of metal carbonyls with
Results and Discussion
Hexafluoroacetone-hydrate which exists as a geminal diol
reacts with cationic isocyanide platinum complexes in the
presence of stoichiometric amounts of triethylamine to af-
ford the corresponding carbamoyl complexes 1-4 in high
yields (eq. (2)) [22].
OHϪ
Ϫ
[Pt(Cl)(CϵNR)(PPh3)2]ϩ(BF4)Ϫ
Ǟ
N3 and vice versa that of azido complexes with free CO
[27] as well as Ϫ less directly Ϫ that of the system azide/
isocyanide [28].
(F3C)2CO·1,5H2O/NEt3
(2)
[Pt(Cl){C(ϭO)-NHR}(PPh3)2]
1Ϫ4
The compounds are clearly identified by their character-
istic IR absorptions and correct elemental analyses. Of
compound 5 all elements were determined with the excep-
tion of phosphorus; also the mass spectrum could be re-
corded which revealed the parent peak (Experimental Part).
Two additional weak signals have been assigned to the mo-
lecular peaks of [PtCl2(PPh3)2] and [Pt(NCO)2(PPh3)2]; as
5 turned out to be pure by thin-layer chromatography, how-
ever, the disproportionation must have occurred in the
mass spectrometer.
The characteristic IR absorptions of the -C(ϭO)NH-
group in 1-4 appear at 1585Ϫ1600 cmϪ1 (νCϭO ϩ δNH),
in full accordance with the findings in other complexes of
the type [Pt(Cl){C(ϭO)-NHR}(PPh3)2] which have been
prepared by different routes [5]. The isocyanato complex 5
exhibits very characteristic, strong νasNCO and νsNCO IR
absorptions at 2244 and 1350 cmϪ1, respectively. In com-
parison, for [Pt(NCO)2(PPh3)2] the corresponding IR ab-
sorptions were observed at 2234 and 1313 cmϪ1 [23].
R
1
2
3
4
CH2CO2Et
CH2Ph
C6H11
CH2SO2C6H4-p-Me
For the 1,2-addition of OHϪ to the isocyano function,
a process via a cyclic intermediate of the type A is tenta-
tively suggested. The reactions of the complexes
[Pt(Cl)(CϵNR)(PPh3)2]ϩ(BF4)Ϫ (R ϭ Me, CHϭCH2) with
(F3C)2CO·1.5H2O/NEt3 only gave mixtures from which
mainly [PtCl2(PPh3)2] was isolated [19]. No reaction at all
occurred with the neutral complexes [PtCl2L(PPh3)] con-
taining vinylogous isocyanoamine (CϵN-CϭC-N<) li-
gands [18].
Experimental Part
The starting materials [Pt(Cl)(CNR)(PPh3)2](BF4) (R ϭ CH2Ph,
CH2SO2C6H4-p-Me) [15] and [Pt(Cl)(CNNR2)(PPh3)2](BF4) [24]
were prepared from [(Ph3P)2Pt(μ-Cl)2Pt(PPh3)2](BF4)2 [29] and the
respective isocyanide according to published procedures. The ex-
perimental data of 2 and 4 were already reported in [15].
A
[Pt(Cl)(CNCH2CO2Et)(PPh3)2](BF4):
A
solution of 1.33 g
We also studied the reactions of the N-isocyanide com-
(11.76 mmol) of CNCH2CO2Et in 30 ml of chloroform is added
dropwise with stirring to a suspension of 9.90 g (5.88 mmol) of
[(Ph3P)2Pt(μ-Cl)2Pt(PPh3)2](BF4)2 in 50 ml of the same solvent. In
the end the suspension has largely cleared up and is filtered through
Celite. The pale yellow filtrate is concentrated in vacuum to about
half the volume, layered carefully with 40 ml of diethylether and
cooled to 0 °C. The compound separates as colourless rod-shaped
Ϫ
plexes trans-[Pt(Cl)(CϵN-NR2)(PPh3)2]ϩBF4 (R ϭ Et,
Pri, 2R ϭ C
TH(Me)(CH2)3CUH(Me)) [24] with (F3C)2CO·1,5
H2O/NEt3 which should lead to the unknown carbazoyl li-
gand [M-C(ϭO)-NH-NR2]. In all three cases, however, an
identical product has been obtained and recognized as the
isocyanato complex 5 (eq. (3)).
Z. Anorg. Allg. Chem. 2008, 1002Ϫ1004
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1003

W. P. Fehlhammer, K. Bartel, R. Metzner, W. Beck
crystals which are washed with ether and dried in high vacuum.
Yield 10.0 g (89 %). M.P. 194 °C; C41H37BClF4NO2P2Pt (955.04):
Found C 50.93, H 3.79, N 1.40; Calc. C 51.56, H 3.90, N 1.47 %.
IR (KBr, cmϪ1): 3070 sh, 3055 w, 2985 w, 2940 vw (νCH), 2266 s (νCN),
1756 vs (νasCO2), 1215 s (νsCO2), 1055 vs, br (νasBF4), 342 w (νPtCl); Ϫ 1H
NMR (δ, CDCl3): δ ϭ 2.2 (t, 3H, C2H5), 3.74 (t, 2H, CH2), 3.9 (9, 2H,
C2H5), 7.47 (m, 30H, Ph).
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a solution of 1.0 mmol of
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[Pt(Cl)(CNR)(PPh3)2](BF4) in 10 ml of dichloromethane are added
1.2 mmol (121 mg) of triethylamine and 1.1 mmol (212 mg) of
hexafluoroacetone-sesquihydrate. The mixture is allowed to stand
in the dark for 1 d after which time the solvent is removed in vac-
uum and the residue recrystallized from dichloromethane/acetone
and diethylether. Yield 80 %.
1: M.P. 174 °C (dec.); C41H38ClNO3P2Pt (885.25): Found C 55.73,
H 4.02, N 1.60; M 877.5 in CHCl3; Calc. C 55.65, H 4.33, N
1.58 %.
IR (KBr, cmϪ1): 3435 sh, 3390 m (νNH), 3075 sh, 3050 m, 2985, 2930,
2895 w (νCH), 1735 sh, 1724 s (νasCO2), 1594 vs, 1585 sh (νCϭO and δNH),
1224 sh, 1178 s (νsCO2), 1156 sh.
´
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Angew. Chem. Int. Ed. Engl. 1974, 13, 599.
3: M.P. 194 °C (dec.); C43H42ClNOP2Pt (881.30): Found C 58.03,
H 4.50, N 1.44; Calc. C 58.60, H 4.80, N 1.59 %.
IR (KBr, cmϪ1): 3425 m (νNH), 3075 sh, 3055 m, 2925 s, 2850 m (νCH),
1600 s, 1586 sh, 1570 sh (νCϭO and δNH), 1188 sh, 1157 m-s.
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[Pt(Cl)(CNNR2)(PPh3)2](BF4) in 20 ml of dichloromethane are ad-
ded 1.1 mmol of triethylamine and 1.1 mmol of hexafluoroacetone-
sesquihydrate. The mixture is stirred and after 10 min pale yellow
crystals start to separate. The mixture is concentrated to about
5 ml, and the solid is filtered off and recrystallized several times
from dichloromethane. Yield 86 %.
M.P. 242 °C; C37H30ClNOP2Pt (797.13): Found C 55.42, H 3.83,
N 1.80, O 2.38, Cl 4.17, Pt 23.04; Calc. C 55.75, H 3.79, N 1.76,
O 2.01, Cl 4.45, Pt 24.47 %.
IR (KBr, cmϪ1): 2244 vs (νasNCO), 1350 vs (νsNCO); the absence of any IR
bands about 550 cmϪ1 points to trans-configuration as in the starting
complex [30]. Ϫ MS (m/z (%)): 797 (3) [Mϩ], 755 (10) [Mϩ-NCO], 719 (26)
[Mϩ-NCO-Cl].
[22] Complexes 2 and 4 have been reported briefly (cf. lit. [15]).
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