Synthesis, structure and reactivity of N,O-metallacyclic (dicarbonyldiazene) platinum complexes

Article abstract of DOI:10.1039/a709198b

Reaction of cis-Pt(PR¹₃)₂Cl₂ (R¹ = Me, Ph) with diacyl hydrazine R²OCNHNHCOR² (R² = Me, Ph) in refluxing ethanol and NaHCO₃ afforded platinum diazene diacyl complexes Pt(PR¹₃)₂(R²OCNNCOR²) (1, R¹ = R² = Ph; 3, R¹ = Me, R² = Ph; 4, R¹ = R² = Me). Reaction of Pt(PPh₃)₂(C₂H₄) with diazene dicarboxylates R²OCNNCOR² (R² = OEt, OPrⁱ) resulted in the formation of Pt(PPh₃)₂(R²OCNNCOR²) (2, R² = OEt; 5, R² = OPrⁱ). Multinuclear NMR spectroscopy on 1-5 revealed that the dicarbonyl-substituted diazene ligand is coordinated asymmetrically, consistent with a five membered Pt-N-N-C-O ring. Compound 5 crystallises from THF-benzene as the solvate Pt(PPh₃)₂(PrⁱO₂CNNCO ₂Prⁱ)·(C₆H₆)₂; its X-ray crystal structure shows that the coordination sphere of platinum is essentially square planar and coplanar with the five membered Pt1-O1-C5-N2-N1 ring. The Pt1-O1 distance is 2.027(4) A and the Pt1-N1 distance is 2.050(5) A. The N1-N2 distance is 1.421(6) A while the N2-C5 and C5-O1 distances are 1.273(7) and 1.314(7) A, respectively. Complexes 1-5 show sensitivity towards chlorinated solvents (CH₂Cl₂, CHCl₃) under photolysis conditions, forming the corresponding cis-platinum bis(phosphine) dichloride complexes; the same products are formed in a slower thermal reaction with 2 and 5. Complexes 2 and 5 react photochemically with ethylene in [²H₈]THF yielding Pt(PPh₃)₂(C₂H₄) but 1, 3 and 4 are inert. Addition of an excess of dppe ligand to 2 and 5 resulted in the displacement of PPh₃ and the formation of Pt(dppe)(EtO₂CNNCO₂Et) and Pt(dppe)(PrⁱO₂CNNCO₂Prⁱ) [dppe = 1,2-bis(diphenylphosphino)ethane].

Full text of DOI:10.1039/a709198b

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Synthesis, structure and reactivity of N,O-metallacyclic
(dicarbonyldiazene) platinum complexes
Danny Chan,a Leroy Cronin,a Simon B. Duckett,a Peter HupÐeldb and Robin N. Perutz*,a
a Department of Chemistry, University of Y ork, Y ork, UK Y O1 5DD
b Dow Corning L td, Barry, S. Glamorgan, UK CF6 7Y L
Reaction of cis-Pt(PR1 ) Cl (R1 \ Me, Ph) with diacyl hydrazine R2OCNHNHCOR2 (R2 \ Me, Ph) in
3 2
2
reÑuxing ethanol and NaHCO a†orded platinum diazene diacyl complexes Pt(PR1 ) (R2OCNNCOR2) (1,
3
3 2
R1 \ R2 \ Ph; 3, R1 \ Me, R2 \ Ph; 4, R1 \ R2 \ Me). Reaction of Pt(PPh ) (C H ) with diazene
3 2
2 4
dicarboxylates R2OCNNCOR2 (R2 \ OEt, OPri) resulted in the formation of Pt(PPh ) (R2OCNNCOR2) (2,
3 2
R2 \ OEt; 5, R2 \ OPri). Multinuclear NMR spectroscopy on 1È5 revealed that the dicarbonyl-substituted
diazene ligand is coordinated asymmetrically, consistent with a Ðve membered PtwNwNwCwO ring.
Compound 5 crystallises from THFÈbenzene as the solvate Pt(PPh ) (PriO CNNCO Pri) É (C H ) ; its X-ray
3 2
2
2
6 6 2
crystal structure shows that the coordination sphere of platinum is essentially square planar and coplanar with
the Ðve membered Pt1wO1wC5wN2wN1 ring. The Pt1wO1 distance is 2.027(4) A and the Pt1wN1 distance
is 2.050(5) A. The N1wN2 distance is 1.421(6) A while the N2wC5 and C5wO1 distances are 1.273(7) and
1.314(7) A, respectively. Complexes 1È5 show sensitivity towards chlorinated solvents (CH Cl , CHCl ) under
2
2
3
photolysis conditions, forming the corresponding cis-platinum bis(phosphine) dichloride complexes; the same
products are formed in a slower thermal reaction with 2 and 5. Complexes 2 and 5 react photochemically with
ethylene in [2H ]THF yielding Pt(PPh ) (C H ) but 1, 3 and 4 are inert. Addition of an excess of dppe ligand to
8
3 2
2
3
4
2 and 5 resulted in the displacement of PPh and the formation of Pt(dppe)(EtO CNNCO Et) and
2
2
Pt(dppe)(PriO CNNCO Pri) [dppe \ 1,2-bis(diphenylphosphino)ethane].
2
2
There are, in general, two ways in which a diazene (or azo)
ligand can coordinate to transition metals.1 The usual mode
requires the diazene group to utilise its lone pair(s) on the
nitrogen atom(s) (often the HOMO) to form r bond(s) with
the metal. This method of coordination can generate both
mononuclear and binuclear complexes.1,2 The second mode
involves the symmetrical binding of the diazene moiety to the
metal by the transfer of electron density from the NxN p-
bonding molecular orbital to the metal and from the metal to
the NxN p-anti-bonding molecular orbital.3
dicarboxylate compounds Pt(PPh ) (EtO CNNCO Et) 2 and
3 2
2
2
Pt(PPh ) (PriO CNNCO Pri) 5. A crystal structure of 5 has
3 2
2
2
been obtained, which provides unambiguous evidence on the
binding mode of the diazene dicarboxylate ligand to the plati-
num centre. These compounds were synthesised in order to
test their photochemical properties.
Results
Preparation of Pt(PR1 ) (R2OCNNCOR2) complexes (1,
3 2
Introduction of substituents other than simple alkyl or aryl
groups into the diazene compound can provide additional
R1 = R2 = Ph; 3, R1 = Me, R2 = Ph; 4, R1 = R2 = Me)
The procedure reported by Dilworth and Kasenally9 for the
coordination sites for the metal.
A carbonyl-substituted
preparation of the complex Pt(PPh ) (PhOCNNCOPh) 1 was
diazene compound, for instance, can bind through oxygen as
well as a diazene nitrogen.4,5 Ittel and Ibers have shown by
X-ray crystallography that the azo ligand in the complex
3 2
used to synthesise two analogues: Pt(PMe ) (PhOC-
3 2
NNCOPh) 3 and Pt(PMe ) (MeOCNNCOMe) 4. Reaction of
3 2
the cis-platinum bis(phosphine) dichloride complex with the
Pt(PPh ) (PhOCNNCOPh) 1 coordinates to the metal as a
3 2
appropriate diacyl hydrazine in reÑuxing ethanol, in the pres-
metallacycle, binding to the metal through one oxygen and
ence of NaHCO , yielded air-stable crystals of the platinum
complex after work up (60È70% yield, eqn. 1).
one nitrogen atom to form a Ðve-membered ring.6 Bond
lengths from the crystal structure of 1 revealed that the NxN
double bond had lengthened to that of a single bond and one
of the CwN bonds had shortened to a CxN bond when
compared to the free ligand. Thus, this form can be described
as a PtII complex with a substituted hydrazido ligand. Stone
and co-workers in the late 1960s postulated that
Pt(PPh ) (EtO CNNCO Et) 2 adopts a symmetrical struc-
3
3 2
2
2
ture, where the diazene dicarboxylate ligand is coordinated to
the metal in a g2 fashion.7 Cenini and co-workers later
revealed that 2 contains two inequivalent phosphorus nuclei,8
indicating that the diazene dicarboxylate ligand in 2 coordi-
nates to platinum in the same way as the diazene dibenzoyl
ligand found in 1.
We
report
here
the
full
characterisation
of
We have also synthesised 1 by the same method in order to
obtain comparative spectroscopic data. All the above com-
plexes are highly soluble in benzene, THF and chlorinated sol-
vents. Multinuclear NMR characterisation of complexes 1, 3
Pt(PMe ) (PhOCNNCOPh)
NNCOMe) 4, the trimethylphosphine analogues of 1. We
have also developed a new route to the platinum diazene
3
and Pt(PMe ) (MeOC-
3 2
3 2
New J. Chem., 1998, Pages 511È516
511

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Table 1 1H and 31P M1HN NMR (295 K) spectroscopic data of complexes 1È7
Compound
1H, d (J/Hz)
31P, d (J/Hz)a
1b
7.00È8.00 (m, Ph)
3.1 [d, PO, J(PP) \ 22, J(PtP) \ 3685]
17.5 [d, PN, J(PP) \ 22, J(PtP) \ 3261]
6.2 [br d, PO, J(PtP) B 3790]
2c
1.14 (3H, br t, CH CH )
2
3
1.35 [3H, t, CH CH , J(HH) \ 7.0]
16.6 [d, PN, J(PP) \ 23, J(PtP) \ 3166]
2
3
4.12 (2H, br, CH CH )
2
3
4.57 [2H, quart, CH CH , J(HH) \ 7.0]
2
3
7.00È8.00 (30H, m, Ph)
3b
4b
1.80 [9H, d, PMe , J(PH) \ 11.0]d
[20.1 [d, PO, J(PP) \ 26, J(PtP) \ 3435]
[10.9 [d, PN, J(PP) \ 26, J(PtP) \ 3028]
3
1.90 [9H, d, PMe , J(PH) \ 11.3]d
3
7.00È8.00 (10H, m, Ph)
1.70 [9H, d, PNMe , J(PH) \ 10.7]d
[38.0 [d, PO, J(PP) \ 27, J(PtP) \ 3448]
[29.0 [d, PN, J(PP) \ 27, J(PtP) \ 3010]
3
1.80 [9H, d, POMe , J(PH) \ 11.2]d
3
2.01 [3H, d, COMe, J(PH) \ 0.9]
2.23 (3H, s, COMe)
5e
0.75 [6H, d, CH(CH ) , J(HH) \ 6.2]
5.8 [d, PO, J(PP) \ 23, J(PtP) \ 3859]
16.5 [d, PN, J(PP) \ 23, J(PtP) \ 3158]
3 2
1.06 [6H, d, CH(CH ) , J(HH) \ 6.2]
3 2
4.08 [1H, sept, CH(CH ) , J(HH) \ 6.2]
3 2
4.12 [1H, sept, CH(CH ) , J(HH) \ 6.2]
3 2
7.00È8.00 (30H, m, Ph)
6c
7c
0.97 [3H, t, CH CH , J(HH) \ 7.2]
31.1 [d, PO, J(PP) \ 11, J(PtP) \ 3839]
38.1 [d, PN, J(PP) \ 11, J(PtP) \ 3041]
2
3
1.23 [3H, t, CH CH , J(HH) \ 7.2]
2
3
4.00 [2H, d, CH CH , J(HH) \ 7.2]
2
3
4.62 [2H, d, CH CH , J(HH) \ 7.2]
2
3
1.10 [6H, d, CH(CH ) , J(HH) \ 6.2]
31.0 [d, PO, J(PP) \ 12, J(PtP) \ 3843]
38.1 [d, PN, J(PP) \ 12, J(PtP) \ 3023]
3 2
1.36 [6H, d, CH(CH ) , J(HH) \ 6.2]
3 2
4.79 [1H, sept, CH(CH ) , J(HH) \ 6.2]
3 2
5.40 [1H, sept, CH(CH ) , J(HH) \ 6.2]
3 2
7.00È8.00 (30H, m, Ph)
a Couplings to Pt refer to the satellites from 195Pt; PO indicates phosphorus trans to oxygen and PN indicates phosphorus trans to nitrogen. b In
CDCl . c In C D . d Contain overlapping satellites from 195Pt. e In [2H ]THF.
3
6
6
8
R2
and 4 (Tables 1 and 2) supports the coordination of the
diazene ligand R2OCNNCOR2 (R2 \ Me, Ph) to the plati-
num centre via the oxygen and nitrogen atoms (Scheme 1) as
in the crystal structure of 1.6
1 R1 = R2 = Ph
R13P
R13P
O
N
2 R1 = Ph; R2 = OEt
3 R1 = Me; R2 = Ph
4 R1 = R2 = Me
Pt
N
5 R1 = Ph; R2 = OPri
R2
The 31P M1HN NMR spectrum of 4 in CDCl shows two
O
3
inequivalent phosphorus nuclei that are mutually coupled and
Scheme 1
nucleus trans to the oxygen donor and the resonance at d
possess 195Pt satellites (Fig. 1). The two 1J(PtP) coupling con-
stants of 4 di†er by about 400 Hz. Generally, a phosphorus
nucleus trans to an oxygen donor has a larger 1J(PtP) value
compared to a phosphorus nucleus trans to a nitrogen
donor.10 Following this general trend we can assign the reso-
P
[29.0 [1J(PtP) \ 3010 Hz] to the phosphorus nucleus trans
to the nitrogen donor. The 1H NMR spectrum of 4 in CDCl
3
shows the two methyl resonances on the diazene diacyl ligand
nance at d [ 38.0 [1J(PtP) \ 3448 Hz] to the phosphorus
as a singlet at d 2.23 and a doublet at d 2.01 [5J(PH) \ 0.9
Hz]. The two PMe groups appear as separate doublets at d
P
H
H
3
H
1.70 and d 1.80, each possessing overlapping 195Pt satellites.
H
On selective phosphorus decoupling at d [ 38 (phosphorus
P
trans to oxygen) the doublet resonances at d 2.01 (COMe)
H
Table 2 13C M1HN NMR (295 K) spectroscopic data of complexes 1
and 3–5
and d 1.80 (PMe ) in the 1H NMR spectrum collapse into
H
3
singlets. On selective phosphorus decoupling at d [ 29
Compound
d (J/Hz)a
P
(phosphorus trans to nitrogen), only the doublet resonance at
1b
127.1È135.2 (Ph)
d
1.70 (PMe ) in the 1H NMR spectrum collapses into a
singlet. Hence the resonance at d 1.70 is due to the PMe
trans to nitrogen and the resonance at d 1.80 is due to the
PMe trans to oxygen. On changing the solvent to C D we
observe a substantial downÐeld shift of the diazene diacyl
methyl resonances and an upÐeld shift of the PMe doublets,
with increased separation between them.
163.2 [dd, CO, J(PC) \ 10, 3]
H
3
171.7 [d, CO, J(PC) \ 4]
H
3
3b
4b
16.6 [d, PCH , J(PC) \ 38, J(PtC) \ 33]
H
3
19.7 [dd, PCH , J(PC) \ 44, 2; J(PtC) \ 43]
3
3
6 6
124.2È131.8 (Ph)
163.4 [dd, CO, J(PC) \ 9, 3]
174.6 [d, CO, J(PC) \ 4]
3
16.3 [d, PCH , J(PC) \ 38, J(PtC) \ 33]
3
The 13C M1HN NMR spectrum of 4 shows two CO reso-
nances at d 175.4 and d 165.4, the former resonance being a
16.5 [d, CH , J(PC) \ 5]
3
19.6 [dd, PCH , J(PC) \ 45, 2; J(PtC) \ 45]
C
C
3
22.1 [d, CH , J(PC) \ 4]
doublet [J(PC) \ 3 Hz] with 195Pt satellites [J(PtC) \ 67
Hz] and the latter a doublet of doublets [J(PC) \ 9 Hz, 4 Hz]
without detectable 195Pt satellites. The diazene diacyl methyl
3
165.4 [dd, CO, J(PC) \ 9, 4]
175.4 [d, CO, J(PC) \ 3, J(PtC) \ 67]
5c
23.8 (s, CH )
carbon atoms can be detected as two doublet resonances at d
3
24.1 (s, CH )
3
C
22.1 [J(PC) \ 4 Hz] and d 16.5 [J(PC) \ 5 Hz].
C
67.6 (s, CH)
The UV/VIS spectra of complexes 1, 3 and 4 show a promi-
71.2 (s, CH)
128.8È136.6 (Ph)
nent low-energy band at around 300 nm (Table 3). Both com-
plexes 1 and 3 show a band maximum at ca. 319 nm, whereas
the band for 4 is shifted 15 nm to higher energy. This e†ect is
observed on changing the diazene from the aryl PhOCNN-
a Couplings to Pt refer to the satellites from 195Pt. b In CDCl . c In
3
[2H ]THF, no CO resonance was detected.
8
512
New J. Chem., 1998, Pages 511È516

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sponds to that found in complexes 1, 3 and 4, co-ordinating
via the nitrogen and oxygen atoms to form a metallacycle.
Multinuclear NMR spectra of Pt(PPh ) (EtO CNNCO Et)
3 2
2
2
2 and Pt(PPh ) (PriO CNNCO Pri) 5 conÐrm that both com-
3 2
2
2
plexes have inequivalent phosphorus atoms as well as inequi-
valent alkyl groups on the diazene ligand (Tables 1 and 2).
The 31P M1HN NMR spectra of 2 and 5 again show two
mutally coupled doublet resonances, both with 195Pt satellites.
The IR spectra of 2 and 5 show CO/CN stretching bands in
the 1610È1670 cm~1 region (Table 3); the bands were more
intense than the corresponding bands of 1, 3 and 4. In the IR
spectrum of 2 two broad peaks are observed at around 1600
cm~1 in dichloromethane, but in nujol we can observe up to
Ðve peaks in the same region. The UV/VIS spectra of 2 and 5
contain low-energy shoulders at ca. 330 and 460 nm (Table 3).
Crystal Structure of Pt(PPh ) (PriO CNNCO Pri) Æ (C H ) 5
Fig. 1 31P M1HN NMR spectrum of Pt(PMe ) (MeOCNNCOMe) (4)
3 2
2
2
6 6 2
3 2
in CDCl (295 K) consisting of two doublets, each with 195Pt satellites
Crystals of 5 suitable for X-ray data collection were grown by
slow evaporation of a 2 : 1 THFÈbenzene solution of 5 at
room temperature. The structure of 5 consists of mono-
molecular units of the complex with two molecules of benzene
per unit cell. The structure of 5 (Fig. 2) clearly shows that the
diazene ligand coordinates to the platinum centre through the
oxygen atom of one carbonyl group and the nitrogen atom of
the diazene function remote from the coordinated carbonyl.
The principal bond lengths and angles (Fig. 3) follow a very
similar pattern to that reported for 1 and related diacyl
diazene metal complexes.4,5,6 The platinacycle contains OwC
and NwN bonds which are extended relative to those of the
free ligand, while the CwN bond is shortened. The platina-
cycle containing Pt, O1, C5, N2 and N1 is planar within 0.012
A and essentially coplanar with the coordinated atoms P1, P2,
O1 and N1 which are planar within 0.037 A. The exocyclic
carbon atom C4 is coplanar with the metallacycle. The phos-
3
COPh ligand to the alkyl MeOCNNCOMe ligand. No such
e†ects are observed on changing the phosphine ligand from
PPh to PMe . Since the crystal structure of 1 shows a conju-
3
3
gated metallacycle,6 we assign this band to a transition of the
metallacycle, rather than attempting to distinguish intra-
ligand transitions from chargeÈtransfer transitions.
Preparation of Pt(PPh ) (R2OCNNCOR2) complexes (2,
3 2
R2 = OEt; 5, R2 = OPri)
Reaction of Pt(PPh ) (C H ) with an equivalent amount or
3 2
2 4
excess (up to threefold) of R2OCNNCOR2 (R2 \ OEt, OPri)
in benzene at room temperature in the absence of light yields
Pt(PPh ) (R2OCNNCOR2) (R2 \ OEt 2, OPri 5) and ethyl-
3 2
ene gas (eqn. 2).
phoruswmetal
bond
lengths
di†er
only
slightly
[dr(PtwP) \ 0.012 A], but there is a substantial di†erence in
the angles to adjacent ligands: P1wPtwN1 \ 97.5(1)¡,
P2wPtwO1 \ 87.1(1)¡.
Reactions of Pt(PR1 ) (R2OCNNCOR2) complexes
3 2
(R1 = Me, Ph; R2 = Me, Ph, OEt, OPri)
Complexes 1, 3 and 4 show no reactivity towards ethylene or
diphenylacetylene when photolysed in [2H ]THF. Photolysis
8
of complexes 1, 3 and 4 in CDCl resulted in the formation of
3
These compounds are yellow/orange in colour and relatively
air stable as solids. They are slightly soluble in benzene and 5
is soluble in THF. Based on the evidence of Cenini et al.8 and
our own, the binding mode of the diazene ligand in 2 corre-
the corresponding cis-platinum bis(phosphine) dichloride
Pt(PR1 ) Cl complexes (R1 \ Ph, Me).
3 2
2
Table 3 UV/VIS and IR data for complexes 1È5
Compound
UV/VIS in THF
k/nm (e/dm3 mol~1 cm~1)
IR, m(CO), m(CN)
m/cm~1
1
2
318 (12000)
1565a
1595a
1618b
1642b
1610c
1621c
1629c
1648c
1668c
1561a
1586a
1576a
1612a
1613c
1635c
333 (3100)
463 (400)
3
4
5
319 (8700)
303 (4500)
337 (3100)
465 (400)
Fig. 2 ORTEP drawing19 of 5 showing non-hydrogen atoms with
thermal ellipsoids at the 30% probability level. The two molecules of
benzene of crystallisation are not shown
a In KBr pellet. b In CH Cl . c In nujol.
2
2
New J. Chem., 1998, Pages 511È516
513

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CwO metallacyclic unit. The structural evidence indicates
that the metallacycle is a fully conjugated planar system. The
diazene ligand is readily displaced photochemically in chlorin-
ated solvents. The diazene dicarboxylate ligand of
Pt(PPh ) (PriO CNNCO Pri) has also been replaced photo-
3 2
2
2
chemically in THF and benzene, but the diazene diacyl com-
plexes proved photostable in these solvents.
Experimental
General
All syntheses and manipulations were carried out under argon
using standard Schlenk and high vacuum techniques. All pre-
parative solvents (Fison AR grade) were dried over sodiumÈ
benzophenone and distilled under argon (chlorinated solvents
were dried over P O , ethanol was dried over magnesium
2
5
metal turnings and iodine). NMR solvents were obtained from
Goss ScientiÐc or Aldrich, and were dried over potassium
metal under argon and distilled on a high vacuum line prior
to use (chlorinated solvents were dried over molecular sieves
or P O ). Chemicals were obtained from the following sources
2
5
and used without further puriÐcation: K PtCl , PPh ,
2
4
3
MeOCNHNHCOMe, PhOCNHNHCOPh, EtO CNNCO Et
and PriO CNNCO Pri were supplied by Aldrich; PMe was
supplied by Strem.
2
2
2
2
3
UV/VIS spectra were recorded on a Perkin-Elmer Lambda
7 spectrophotometer. Infrared spectra were recorded on a
Mattson RS FTIR instrument. Mass spectra were recorded on
a VG Auto-Spec mass spectrometer. NMR spectra were
recorded on a Bruker MSL 300 MHz spectrometer. 1H NMR
spectra (300.13 MHz) were referenced relative to the peaks of
the residual protio solvents: benzene (d 7.15), chloroform (d
7.30), dichloromethane (d 5.30), tetrahydrofuran (d 1.73, d
3.85). 31P M1HN NMR spectra (121.94 MHz) were referenced
to external H PO (85%). 13C M1HN NMR spectra (75.47
Fig. 3 Inner coordination sphere of 5, showing (a) bond distances
(A) and (b) bond angles (degrees)
Both 2 and 5 react thermally with chlorinated solvents at
room temperature to give cis-Pt(PPh ) Cl as the major
3 2
2
product, with 5 being more readily converted. UV irradiation
in CHCl generated the same products more rapidly. Irradia-
3
4
3
MHz) were referenced to the solvent peak: benzene (d 128.0),
dichloromethane (d 54.5), chloroform (d 77.7) and tetra-
hydrofuran (d 25.2, d 67.4). Elemental analyses were performed
by Elemental Microanalysis Ltd, Devon, UK.
tion of 5 with ethylene or diphenylacetylene in [2H ]THF
8
resulted in the formation of Pt(PPh ) (C H ) [d 2.2,
3 2
2
4
H
J(PtH) \ 62 Hz] or Pt(PPh ) (PhCy CPh) [d
35,
3 2
P
J(PtP) \ 3000 Hz].11 However, the same outcome can be
achieved if the mixture is heated at 70 ¡C in the absence of
light.
Photolysis of samples was carried out in sealed Pyrex NMR
tubes (k [ 290 nm) using a Philips HPK 125 W medium pres-
sure mercury lamp at room temperature. Typically, both a
cut-o† Ðlter (295È410 nm) and a water Ðlter were placed in
front of the lamp output. Prior to photolysis, samples were
kept for 24 h at room temperature shielded from ambient
light. Their NMR spectra were then recorded in order to
ensure that there was no competing thermal reaction at room
temperature.
In addition to the organometallic species, some organic
photoproducts are observed on irradiation of 5 in [2H ]THF.
8
Their 1H NMR spectra exhibit similar features to the 1H
NMR data of the photoproducts from the free diazene ligand
PriO CNNCO Pri. Further research to establish their iden-
2
2
tities is in progress. In general, diazene compounds initially
undergo photochemically induced transÈcis isomerisation
prior to degradation, involving the liberation of molecular N
and formation of a radical pair.12 Diacyl diazene compounds
are reported to form the corresponding diketone upon extru-
2
Syntheses
The complexes cis-Pt(PPh ) Cl ,15 cis-Pt(PMe ) Cl 16 and
sion of N on photolysis.13
3 2
2
3 2 2
2
Pt(PPh ) (C H )17 were synthesised according to literature
On addition of an excess of 1,2-bis(diphenylphosphino)-
3 2
2 4
procedures. Mass spectral peaks are quoted only when they
ethane (dppe) to complex 2 or 4, a new singlet resonance was
have a major contribution from 194Pt.
observed in the 31P M1HN NMR spectrum at d [4.7 (free
PPh ) and two new doublet resonances at ca. d 38.1 and d
3
31.1, both with 195Pt satellites, which (Table 1) have been
Preparation of Pt(PPh ) (PhOCNNCOPh) 1. This synthe-
3 2
assigned as Pt(dppe)(EtO CNNCO Et) 6. The complex
sis follows the procedure of Dilworth and Kasenally.9
2
2
Pt(dppe)(PriO CNNCO Pri) 7 is formed similarly. The dis-
Pt(PPh ) Cl (0.20 g, 0.2 mmol) and PhOCNHNHCOPh
2
2
3 2
2
placement of triphenylphosphine with dppe is not uncommon
in platinum complexes; for example, addition of dppe to cis-
Pt(PPh ) Cl in chloroform produces Pt(dppe)Cl in quanti-
(0.06 g, 0.2 mol) were suspended in ethanol (20 mL) with
sodium hydrogen carbonate (0.06 g). The mixture was reÑuxed
under argon for 4 h. During this time the white suspension
gradually dissolved, yielding a yellow solution. The solvent
was removed under vacuum. The crude product was dissolved
in benzene, and hexane was added until precipitation began.
Yellow crystals formed overnight (0.13 g, 70% yield). Mass
spectrum (FAB): m/z 956 (M`, 194Pt, 63%); 957 (M`, 195Pt
and [M ] H]`, 194Pt, 100%).
3 2
2
2
tative yield.14
Conclusion
This paper reports simple synthetic routes to complexes
Pt(PR1 ) (R2OCNNCOR2), containing the PtwNwNw
3 2
514
New J. Chem., 1998, Pages 511È516

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Table 4 Crystallographic data for complex 5
Crystal Data
Empirical formula
M
Temperature/K
Crystal dimensions/mm
Crystal description
Crystal system
Space group
C
H
N O P Pt
4 2
56 56
2
1078.06
293(2)
0.4 ] 0.4 ] 0.4
Brown block
Triclinic
P1 (No. 2)
Unit cell dimensionsa
a \ 15.395(10) A a \ 104.86(3)¡
b \ 15.885(7) A b \ 95.38(3)¡
c \ 11.481(2) A c \ 66.95(3)¡
Volume/A
Z
F(000)
Ž
3
2497(2)
2
1092
1.434
29.21
Density (calcd)/g cm~3
l/cm~1
Data Collection
Di†ractometer
Rigaku AFC6S
Radiation
Wavelength/A
MoKa, graphite monochromated
0.7107
Scan type
x[2h
Scan rate/min~1
16.0¡
Scan width/¡
(1.21 ] 0.30 tan h)
2h range for data collection/¡
ReÑections collected
Independent reÑectionsb
Transmission coefÐcients
Data corrections
5.18È50.02
9336 (including 195 standard reÑections)
8783 [R%(int) \ 3.12]
0.90 (min), 1.00 (max), 0.96 (average)
Lorentz-polarisation
Average intensity change of standard reÑx:
Index ranges
[0.9% (3 reÑections checked every 150 data)
0 O h O 18, [16 O k O 18, [13 O l O 13
Structure solution
Patterson methods with SAPI91c
expanded with DIRDIFd
ReÐnement method
Non-hydrogen atoms
Hydrogen atoms
Full-matrix least-squares on F2 with SHELXL93e
Anisotropic
Riding model, isotropic
Weighting scheme
w \ [r2(F2) ] (0.0457P)2]~1
o
P \ [max(I , 0) ] 2F 2]/3
obs
c
Dataf/restraints/parameters
Data-to-parameter ratio
Goodness-of-Ðtg on F2
R(%)h indices
8783/0/586
14.98
1.00
[I [ 2r(I )]
R1 \ 0.0391, wR2 \ 0.0854
R1 \ 0.0650, wR2 \ 0.0932
o
o
All data
Final di†erence map
Largest di†. peaki and hole/e A
Largest shift/esd in Ðnal cycle
Ž
~3
0.77 and [0.64
0.00
a Unit cell parameters and their esds were determined from a least-squares Ðtting of the setting angles of 20 reÑections in the range
13.96¡ O 2h O 15.82¡. b R(int) \ & o F2 [ F2(mean) o/&[F2]; 358 reÑections measured twice. c Ref. 18(a). d Ref. 18(b). e Ref. 18(c). f Zero reÑections
o
o
o
suppressed in the reÐnement. g GOF \ M&[w(F 2 [ F 2)2]/(n [ p)N1@2 where p \ number of parameters, n \ number of data. h R1 \ &pF o
o
c
o
[ o F p/& o F o. wR2 \ M&[w(F 2 [ F 2)2]/&[w(F 2)2]N1@2. i Located 1.10 A away from Pt(1).
c
o
o
c
o
Preparation
of
Pt(PPh ) (EtO CNNCO Et)
3 2
2.
H, 4.5; N 4.5. Calcd for C
4.9%). Mass spectrum (FAB): m/z 584 (M`, 194Pt, 55%); 585
(M`, 195Pt and [M ] H]`, 194Pt, 100%).
H
N O P Pt: C, 41.0; H, 4.8; N,
2
2
20 28
2
2 2
Pt(PPh ) (C H ) (0.64 g, 0.9 mmol) and EtO CNNCO Et
3 2
2
4
2
2
(0.60 g, 3.4 mmol) were dissolved in benzene (20 mL) under an
atmosphere of argon at room temperature. On mixing the two
compounds together, gas evolved and the solution changed
from yellow to red. Within 1 h of addition, a yellow precipi-
tate began to form. The mixture was shielded from ambient
light and left stirring for 12 h. The product was collected and
recrystallised from ethanol to form yellow crystals (0.53 g,
69% yield) (Found: C, 56.1; H, 4.6; N, 3.1. Calcd for
Preparation of Pt(PMe ) (MeOCNNCOMe) 4. This
complex was prepared by a procedure similar to that of 1. The
product was recrystallised by addition of hexane to a benzene
solution of 4 until precipitation began. The benzeneÈhexane
mixture yielded light brown crystals (65% yield) (Found: C,
26.3; H, 5.4; N, 6.1. Calcd for C
5.2; N, 6.1%). Mass spectrum (FAB): m/z 460, (M`, 194Pt,
53%); 461 (M`, 195Pt and [M ] H]`, 194Pt, 100%).
3 2
H
N O P Pt: C, 26.0; H,
C
H
N O P Pt: C, 56.4; H, 4.5; N, 3.1%). Mass spectrum
10 24
2
2 2
42 40
2 4 2
(FAB): m/z 892 (M`, 194Pt, 18%); 893 (M`, 195Pt and
[M ] H]`, 194Pt, 79%).
Preparation of Pt(PMe ) (PhOCNNCOPh) 3. This
Preparation of Pt(PPh ) (PriO CNNCO Pri) 5. This
3 2
3 2
2
2
complex was prepared by the same procedure as 1. The
complex was prepared as for 2. The product was recrystallised
product was recrystallised by addition of hexane to a benzene
solution of 3 until precipitation began. The benzeneÈhexane
mixture gave light yellow crystals (68% yield) (Found: C, 40.3;
from THF giving orange crystals (70% yield) (Found: C, 57.3;
H, 4.8; N, 3.0. Calcd for C
N, 3.0%). Mass spectrum (FAB): m/z 920 (M`, 194Pt, 12%);
H
N O P Pt: C, 57.3; H, 4.8;
44 44
2
4 2
New J. Chem., 1998, Pages 511È516
515

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3 A. Albini and H. Kisch, T op. Curr. Chem., 1976, 65, 105.
921 (M`, 195Pt and [M ] H]`, 194Pt, 73%).
4 C. P. Marabella, J. H. Enemark, W. E. Newton and J. W. McDon-
ald, Inorg. Chem., 1982, 21, 623.
X-Ray crystallographic study of 5
5 G. Avar, W. Russler and H. Kisch, Z. Naturforsch., T eil B, 1987,
42, 50.
6 S. D. Ittel and J. A. Ibers, Inorg. Chem., 1973, 12, 2290.
7 M. Green, R. B. L. Osborne and F. G. A. Stone, J. Chem. Soc. (A),
1968, 3083.
8 S. Cenini, F. Porta, M. Pizzotti and C. Crotti, J. Chem. Soc.,
Dalton T rans., 1985, 163.
9 J. R. Dilworth and A. S. Kasenally, J. Organomet. Chem., 1973, 60,
203.
10 (a) B. Longato and G. Trovo , Inorg. Chim. Acta, 1992, 192, 13; (b)
Crystals of compound 5 were grown at ambient temperature
by the slow evaporation of a 2 : 1 THFÈbenzene solution. The
resulting crystal was cut to size and mounted on a glass Ðbre
using epoxy cement. X-ray data were collected on a Rigaku
AFC6S di†ractometer. Cell constants and an orientation
matrix for data collection were obtained from a least-squares
reÐnement of the positions of 20 automatically centred reÑec-
tions. Equivalent reÑections were merged, and data were cor-
rected for Lorentz and polarisation factors.
The structure of compound 5 was solved using Patterson
methods with SAPI91 and expanded using Fourier techniques
with DIRDIF. Full-matrix least-squares reÐnement on F2 was
carried out with SHELXL 93. Programs used are given in ref.
18 and 19. All non-hydrogen atoms were reÐned anisotropi-
cally. The hydrogen atoms were reÐned on all structures using
a riding model with isotropic temperature factors 1.2 times
that of their carrier atoms (1.5 times for methyl groups). Crys-
tallographic details are summarised in Table 4.
B. Longato, G. Trovo and G. Valle, J. Chem. Soc., Dalton T rans.,
1993, 669; (c) G. K. Anderson and G. Lumetta, Inorg. Chem., 1987,
26, 1291.
11 R. S. Paonessa, A. L. Prignano and W. C. Trogler,
Organometallics, 1985, 4, 647.
12 P. S. Engel, Chem. Rev., 1980, 80, 99.
13 T. J. Kelly, J. Am. Chem. Soc., 1962, 84, 968.
14 G. K. Anderson, J. A. Davies and D. J. Schoeck, Inorg. Chim.
Acta, 1983, 76, L251.
15 F. R. Hartley, Organomet. Chem. Rev. A, 1970, 6, 119.
16 J. G. Evans, P. L. Goggin, R. J. Goodfellow and J. G. Smith, J.
Chem. Soc. (A), 1968, 464.
17 J. Cook, J. Am. Chem. Soc., 1968, 90, 1464.
CCDC reference number 440/021.
18 (a) F. Hai-Fu, SAPI91, Structure Analysis Programs with Intelli-
gent Control, Rigaku Corporation, Tokyo, Japan, 1993; (b) P. T.
Beurskens, G. Admirral, G. Beurskens, G. Bosman, W. P. Garcia-
Granda, H. O. Gould, J. M. Smits and C. Smykalla, T he DIRDIF
Program System, T echnical Report of the Crystallographic L abor-
atory, University of Nijmegen, The Netherlands, 1992; (c) G. M.
Sheldrick, SHEL XL 93, Program for Crystal Structure ReÐnement.
University of Gottingen, Germany, 1993.
Acknowledgements
We wish to thank EPSRC and Dow Corning for their
support.
19 C. K. Johnson, ORT EP, Report ORNL -5138, Oak Ridge National
References
Laboratory, Oak Ridge, TN, 1976.
1 H. Kisch and P. Holzmeier, Adv. Organomet. Chem., 1992, 34, 67.
2 M. Herberhold and K. Leonhard, Angew. Chem., 1976, 88, 227;
Angew. Chem., Int. Ed. Engl., 1976, 15, 230.
Received in Montpellier, France, 17th November 1997;
Paper 7/09198B
516
New J. Chem., 1998, Pages 511È516