Ortho-Metallated complexes of platinum(ii) and diplatinum(i) containing the carbanions (2-diphenylphosphino)phenyl and (2-diphenylphosphino)-n-tolyl (n = 5, 6)

Article abstract of DOI:10.1039/b702808c

When the ortho-metallated complexes cis-[Pt(κ²-C ₆H₃-5-R-2-PPh₂)₂] (R = H 1, Me 2) are either heated in toluene or treated with CO at room temperature, one of the four-membered chelate rings is opened irreversibly to give dinuclear isomers [Pt₂(κ²-C₆H₃-5-R-2-PPh ₂)₂(-C₆H₃-5-R-2-PPh ₂)₂] (R = H 10, Me 11). A single-crystal X-ray diffraction study shows the Pt...Pt separation in 10 to be 3.3875(4) A. By-products of the reactions of 1 and 2 with CO are polymeric isomers (R = H 13, Me 14) in which one of the P-C ligands is believed to bridge adjacent platinum atoms intermolecularly. In contrast to the behaviour of 1 and 2, when cis-[Pt(κ²-C₆H₃-6-Me-2-PPh ₂)₂] (cis-3) is heated in toluene, the main product is trans-3, and reaction of cis-3 with CO gives a carbonyl complex [Pt(CO)(κ¹-C-C₆H₃-6-Me-2-PPh ₂)(κ²-C₆H₃-6-Me-2-PPh ₂)] 15, in which one of the carbanions is coordinated only through the carbon. Formation of a dimer analogous to 10 or 11 is sterically hindered by the 6-methyl substituent. Comproportionation of 1 or 2 with [Pt(PPh ₃)₂L] (L = PPh₃, C₂H₄) gives diplatinum(i) complexes [Pt₂(-C₆H ₃-5-R-2-PPh₂)₂(PPh₃)₂] (R = H 16, Me 17). An X-ray diffraction study shows that 17 contains a pair of planar-coordinated metal atoms separated by 2.61762(16) A. There is no evidence for the formation of an analogue containing -C₆H ₃-6-Me-2-PPh₂. The axial PPh₃ ligands of 16 are readily replaced by Bu^tNC giving [Pt₂(-2-C ₆H₄PPh₂)₂(CNBu^t) ₂] 18, which is protonated by HBF₄ to form a -hydridodiplatinum(ii) salt [Pt₂(-H)(-2-C₆H ₄PPh₂)₂(CNBu^t)₂]BF ₄ [21]BF₄. The J_PtPt values in [21]BF ₄ and 18, 2700 Hz and 4421 Hz, respectively, reflect the weakening of the Pt-Pt interaction caused by protonation. Similarly, 16 and 17 react with the electrophiles iodine and strong acids to give salts of general formula [Pt₂(-Z)(-C₆H₃-5-R-2-PPh₂) ₂(PPh₃)₂]Y (Y = Z = I, R = H 19⁺, Me 20⁺; Z = H, Y = BF₄, PF₆, OTf, R = H 22 ⁺; Z = H, Y = PF₆, R = Me 23⁺). A single-crystal X-ray diffraction study of [23]PF₆ shows that the cation has an approximately A-frame geometry, with a Pt...Pt separation of 2.7888(3) A and a Pt-H bond length of 1.62(1) A, and that the 5-methyl substituents have undergone partial exchange with the 4-hydrogen atoms of the PPh₂ groups of the bridging carbanion. The latter observation indicates that the added proton of [23]⁺ undergoes a reversible reductive elimination-oxidative addition sequence with the Pt-C(aryl) bonds. The Royal Society of Chemistry.

Full text of DOI:10.1039/b702808c

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ortho-Metallated complexes of platinum(II) and diplatinum(I) containing the
carbanions (2-diphenylphosphino)phenyl and (2-diphenylphosphino)-n-tolyl
(n = 5, 6)
Martin A. Bennett,*a Suresh K. Bhargava,*b Johannes Messelha¨user,a Steven H. Prive´r,b Lee L. Wellinga and
Anthony C. Willisa
Received 26th February 2007, Accepted 9th May 2007
First published as an Advance Article on the web 31st May 2007
DOI: 10.1039/b702808c
When the ortho-metallated complexes cis-[Pt(j2-C6H3-5-R-2-PPh2)2] (R = H 1, Me 2) are either heated
in toluene or treated with CO at room temperature, one of the four-membered chelate rings is opened
irreversibly to give dinuclear isomers [Pt2(j2-C6H3-5-R-2-PPh2)2(l-C6H3-5-R-2-PPh2)2] (R = H 10, Me
˚
11). A single-crystal X-ray diffraction study shows the Pt · · · Pt separation in 10 to be 3.3875(4) A.
By-products of the reactions of 1 and 2 with CO are polymeric isomers (R = H 13, Me 14) in which one
of the P–C ligands is believed to bridge adjacent platinum atoms intermolecularly. In contrast to the
behaviour of 1 and 2, when cis-[Pt(j2-C6H3-6-Me-2-PPh2)2] (cis-3) is heated in toluene, the main
product is trans-3, and reaction of cis-3 with CO gives a carbonyl complex
[Pt(CO)(j1-C-C6H3-6-Me-2-PPh2)(j2-C6H3-6-Me-2-PPh2)] 15, in which one of the carbanions is
coordinated only through the carbon. Formation of a dimer analogous to 10 or 11 is sterically hindered
by the 6-methyl substituent. Comproportionation of 1 or 2 with [Pt(PPh3)2L] (L = PPh3, C2H4) gives
diplatinum(I) complexes [Pt2(l-C6H3-5-R-2-PPh2)2(PPh3)2] (R = H 16, Me 17). An X-ray diffraction
˚
study shows that 17 contains a pair of planar-coordinated metal atoms separated by 2.61762(16) A.
There is no evidence for the formation of an analogue containing l-C6H3-6-Me-2-PPh2. The axial PPh3
ligands of 16 are readily replaced by ButNC giving [Pt2(l-2-C6H4PPh2)2(CNBut)2] 18, which is
protonated by HBF4 to form a l-hydridodiplatinum(II) salt [Pt2(l-H)(l-2-C6H4PPh2)2(CNBut)2]BF4
[21]BF4. The JPtPt values in [21]BF4 and 18, 2700 Hz and 4421 Hz, respectively, reflect the weakening of
the Pt–Pt interaction caused by protonation. Similarly, 16 and 17 react with the electrophiles iodine and
strong acids to give salts of general formula [Pt2(l-Z)(l-C6H3-5-R-2-PPh2)2(PPh3)2]Y (Y = Z = I, R =
H 19+, Me 20+; Z = H, Y = BF4, PF6, OTf, R = H 22+; Z = H, Y = PF6, R = Me 23+). A single-crystal
X-ray diffraction study of [23]PF6 shows that the cation has an approximately A-frame geometry, with
˚
˚
a Pt · · · Pt separation of 2.7888(3) A and a Pt–H bond length of 1.62(1) A, and that the 5-methyl
substituents have undergone partial exchange with the 4-hydrogen atoms of the PPh2 groups of the
bridging carbanion. The latter observation indicates that the added proton of [23]+ undergoes a
reversible reductive elimination–oxidative addition sequence with the Pt–C(aryl) bonds.
gold atoms comprise an eight-membered ring.4,5 These complexes
Introduction
are not accessible by ortho-metallation of PPh3. We have also
shown that substitution of a methyl group in the 6-position,
ortho to the gold-carbon bond, of [Au2(l-2-C6H4PPh2)2] exerts
a marked effect on the course of oxidative addition reactions
with halogens. Whereas the dihalodigold(II) complexes [Au2X2(l-
C6H3-5-R-2-Ph2)2] (X = Cl, Br, I; R = H, Me) rearrange by
coupling of the o-phenylene residues to give P-bonded digold(I)
complexes [Au2X2{l-2,2ꢀ-Ph2P(5,5ꢀ-R2C6H3C6H3)PPh2}],5–7 the
digold(II) complexes in the 6-methyl series, [Au2X2(l-C6H3-6-
Me-2-Ph2)2], isomerise rapidly to gold(I)–gold(III) complexes in
which one of the cyclometallated ligands is chelated to gold(III)
(Scheme 1).7 No C–C coupling is observed in the 6-methyl series,
presumably because steric repulsion between the methyl groups
raises the energy of the transition state to reductive elimination of
the two aryl groups.8
The bifunctional, carbanionic ligand [2-C6H4PPh2]− is most often
generated by C–H activation (ortho-metallation) of triphenylphos-
phine in its complexes of the later d-block elements. Although
it behaves mostly as a chelate (j2P,C) ligand, forming a four-
membered ring, there are well-established examples of bridging
behaviour (l-jPjC), and of interconversion between the two
modes.1
We have previously employed transmetallation from the organo-
lithium reagent 2-LiC6H4PPh2 to prepare chelate complexes of
platinum(II) and rhodium(III), [M(j2-2-C6H4PPh2)n] (M = Pt, n =
2; M = Rh, n = 3)2,3 and a binuclear gold(I) complex, [Au2(l-2-
C6H4PPh2)2], in which the bridging ortho-metallated units and the
aResearch School of Chemistry, Australian National University, Canberra,
ACT 0200, Australia
In view of these results, we wondered whether 5- or 6-
methyl substitution would influence, electronically or sterically,
bSchool of Applied Sciences (Applied Chemistry), RMIT University, GPO
Box 2476V, Melbourne, Victoria 3001, Australia
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four-membered chelate rings;12 the coupling constants are lower
than the expected value of 1800–2100 Hz for P trans to r-aryl in
planar platinum(II) complexes,13,14 presumably as a consequence
of ring strain.
The solid state 31P NMR spectrum of 2 shows two overlapping
singlets of almost equal intensity, with 195Pt satellites, at d −53.2
(JPtP 1362 Hz) and −54.5 (JPtP 1355 Hz), which presumably
correspond to the crystallographically inequivalent phosphorus
atoms observed in the X-ray structure (see below). Similar
observations of inequivalent phosphorus resonances in solid state
31P NMR spectra have been made for cis-[PtCl2{Ph2(CH2)nPPh2}]
(n = 1–5)15 and cis-[PtCl2(PPh3)2].16
The presence of two four-membered chelate rings in 2 and 3 has
been confirmed by single-crystal X-ray structural analysis. The
molecular structures are shown in Fig. 1 together with selected
bond lengths and angles. The coordination about platinum in
both complexes is distorted square planar. In 3 the ortho-methyl
substituents lie above and below the P–Pt–P plane. The Pt–
Scheme 1
˚
C distance in 3 [2.095(3) A] is slightly greater than those in 2
the chemistry of [Pt(j2-C6H4PPh2)2] 1.2,3 The results are reported
here, together with more details of the chemistry of 1.
˚
˚
˚
[2.062(3) A, 2.058(4) A] and 1 [2.063(2) A], presumably because
of steric crowding by the ortho-methyl groups; the Pt–P distances
˚
˚
˚
˚
in 3 [2.2799(8) A], 2 [2.306(1) A, 2.3034(9) A] and 1 [2.297(1) A]
do not differ significantly. The bite angles of the chelate ligands in
1–3 are within the range 68–69◦ that is typical of ortho◦-metallated
PPh3 complexes.1 However, the C–Pt–C angle in 3 (111 ) is slightly
greater than those in 1 and 2 (106◦, 105◦), and the P–Pt–P angle in
3 (113◦) is correspondingly less than that in 1 and 2 (116◦, 117◦).
Results and discussion
Analogous to the previously reported preparation of [Pt(j2-
C6H4PPh2)2] 1,8,9 treatment of the lithio-derivatives LiC6H3-5-
Me-2-PPh2 and LiC6H3-6-Me-2-PPh2 with [PtCl2(SEt2)2] gave
the corresponding bis(chelate) complexes cis-[Pt(j2-C6H3-n-Me-
2-PPh2)2] (n = 5 2; n = 6 3) as colourless, air- and moisture-
stable solids in yields of ca. 80% and 50%, respectively. The IR
spectra of 2 and 3, like that of 1, show bands characteristic of
ortho-metallated PPh3 complexes at ca. 1560 and 725 cm−1,9–11 and
the EI-mass spectra both show the same parent-ion peak. The
31P NMR spectra of 2 and 3 consist of singlets with 195Pt satellites
at d −52.5 (JPtP 1352 Hz) and −62.9 (JPtP 1370 Hz), respectively,
the parameters for 2 being almost identical with those previously
reported for 1. The shieldings are characteristic of 31P nuclei in
Oxidative addition reactions of 2 and 3
These are summarised in Scheme 2. Like complex 1, 2 reacts
with one equivalent each of Cl2 (via PhICl2), Br2 and I2, and
with an excess of MeI, to give the platinum(IV) oxidative addition
products [PtXY(j2-C6H3-5-Me-2-PPh2)2] (X = Y = Cl 4, Br 5,
I 6; X = Me, Y = I 7), most of which have been isolated and
characterised by elemental analysis, EI-mass spectroscopy and
NMR spectroscopy. The 31P NMR data (see Experimental) serve
Fig. 1 Molecular structures of cis-[Pt(j2-C6H3-n-Me-2-PPh2)2], n = 5 (2), 6 (3). Ellipsoids show 30% probability levels and hydrogen atoms have been
◦
1
2
˚
deleted for clarity. Asterisks indicate atoms generated by crystallographic symmetry (1 − x, y, − z). Selected bond lengths (A) and angles ( ): 2:
Pt(1)–P(1) 2.306(1), Pt(1)–P(2) 2.3034(9), Pt(1)–C(2) 2.062(3), Pt(1)–C(21) 2.058(4), P(1)–Pt(1)–C(2) 68.9(1), P(2)–Pt(1)–C(21) 68.6(1), P(1)–Pt(1)–C(21)
173.8(1), P(2)–Pt(1)–C(2) 173.7(1), P(1)–Pt(1)–P(2) 117.37(3), C(2)–Pt(1)–C(21) 105.1(1). 3: Pt(1)–P(1) 2.2799(8), Pt(1)–C(2) 2.095(3), P(1)–Pt(1)–C(2)
68.44(9), P(1)–Pt(1)–C(2*) 174.02(8), P(1)–Pt(1)–P(1*) 113.00(4), C(2)–Pt(1)–C(2*) 110.77(17).
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Table 1 31P NMR parameters for [Pt2(j2-C6H3-n-R-2-PPh2)2(l-C6H3-n-
R-2-PPh2)2] (n = 5, R = H 10, Me 11; n = 6, R = Me 12)a,b
10
11
12
d(PA)
d(PB)
24.1
25.6
22.4
−60.7
2040
1235
4
−60.0
2030
1219
5
−64.9
2005
1235
1
J(AX)
J(BX)
J(AAꢀ)
J(BBꢀ)
J(AXꢀ)
J(BXꢀ)
J(AB)
J(ABꢀ)
0
0
0
−150
−141
−122
0
0
0
16
−10
16
−9
18
−9
a Labelling of nuclei: B(A)X–Xꢀ(Aꢀ)Bꢀ, where PA, PA are the 31P nuclei of
Scheme 2
ꢀ
the bridging ortho-metallated ring, PB, PB are the 31P nuclei of the chelating
ꢀ
ortho-metallated ring, and X = 195Pt. J(XXꢀ) could not be determined. b 10
to establish the ligand dispositions and are similar in most cases
to those of the corresponding adducts of 1.3
and 11 in C6D6, 12 in toluene.
In the dichloro complex 4, the added chlorine atoms are
mutually trans; no cis-dichloro isomer was formed, even after
solutions of 4 in CH2Cl2 had been allowed to stand for several days
at room temperature or solutions in toluene had been held at
◦
100 C for 24 h. In contrast, the isolated di-iodo complex 6 has
mutually cis-iodine atoms, one being trans to P and the other trans
to Caryl. No intermediate trans isomer was detected, unlike the
corresponding reaction of iodine with 1.3 The bromo complex 5
also appears to be mainly the cis-isomer but, as in the bromination
of 1,3 it was contaminated by a chelate phosphine oxide complex
formulated as cis-[PtBr2(j2-C6H3-5-Me-2-PPh2){j2-O,C-C6H3-5-
Me-2-P(O)Ph2}]. Complex 7 contains mutually trans-iodo and
-methyl groups; it appears not to isomerise rapidly to the cis-
isomer, unlike the methyl iodide adduct of 1.3
Scheme 3
is even less than that in 1 or 2, whereas JPtP for the phosphorus
in the eight-membered rings (ca. 2030 Hz) is in the usual range
(1800–2100 Hz) for P trans to r-aryl.13,14
The molecular structure of 10, determined by single-crystal
X-ray diffraction, is shown in Fig. 2 together with selected metrical
data. It confirms the conclusions drawn from the spectroscopic
data. Each platinum atom is in a distorted square planar en-
vironment formed by a pair of cis-phosphorus and cis-carbon
atoms; one each of these atoms forms part of a four-membered
chelate ring, the other two constitute with the two metal atoms
a boat-shaped eight membered ring. The distance between the
Treatment of 3 with one equivalent of PhICl2 affords the
trans-dichloro oxidative addition product [PtCl2(j2-C6H3-6-Me-
2-PPh2)2], trans-8 as a pale yellow solid. In contrast to 4, however,
this isomerises completely in CH2Cl2 over a period of hours to the
corresponding cis-isomer (Scheme 2), presumably to relieve steric
crowding of the 6-methyl groups in the ortho-metallated rings.
The reaction of 3 with methyl iodide is far less clean than that
of 2, giving rise to numerous peaks in the regions d 10–30 and
50–95 of the 31P NMR spectrum, perhaps indicative of disruption
of the four-membered rings of 3. However, the main identifiable
product, formed in ca. 30% yield, appears to the expected trans-
(iodo)(methyl)platinum(IV) adduct 9, which is accompanied by
unchanged cis-3 and its trans-isomer (see below).
˚
platinum atoms [3.3875(4) A] is less than that in the structurally
similar arsenic compound [Pt2(j2-C6H3-5-Me-2-AsPh2)2(l-C6H3-
5-Me-2-AsPh2)2] [3.4208(3) A]17 and may indicate a weak attractive
˚
interaction between the 5d8 metal centres.18 This small difference
may also be due to other factors, for example, the smaller size
of phosphorus compared to arsenic. The bite angle in the P–C-
chelate ring [68.8(1)◦] is similar to those in 1–3. Although the Pt–
C distances in the four- and eight-membered rings do not differ
Thermolysis of the bis(chelate) complexes
When colourless solutions of 1 or 2 in toluene are heated
under reflux for 24–48 h, their colour changes to yellow and
dinuclear isomers of 1 or 2, [Pt2(j2-C6H3-5-R-2-PPh2)2(l-C6H3-
5-R-2-PPh2)2] (R = H 10, Me 11) can be isolated in high yield
(Scheme 3). Complex 11 shows a peak at m/z 1491 in the MALDI-
mass spectrum corresponding to [M + H]+ for the dimer. The
31P NMR spectra of 10 and 11 consist of two equally intense
multiplets, with 195Pt satellites, at ca. d −60 and 25, suggestive of
a pair of phosphorus atoms in two four-membered chelate rings
and a pair in one eight-membered ring formed from bridging P–C
ligands. Analysis of the spectra as an AAꢀMMꢀXXꢀ spin system
provided the coupling constants listed in Table 1. The magnitude
of JPtP for the phosphorus atoms in the chelate rings (ca. 1200 Hz)
˚
greatly [2.075(5), 2.060(5) A, respectively], the Pt–P distance in
˚
the four-membered ring [2.321(1) A] of 10 is significantly greater
than that in the presumably less strained eight-membered ring
[2.297(1) A], thus reproducing the trend in the values of JPtP
Surprisingly, it is also greater than the Pt–P distances in the four-
˚
.
membered rings of 1–3.†
† A less precise structural determination of a different crystalline modifi-
cation of 10 has been carried out at 296(2) K on a Philips PW 1100/20
diffractometer using Mo Ka radiation.62 This form is monoclinic, space
group P21/a, with a 25.380(2), b 19.842(2), c 14.050(2) A, b 99.543(11) ,
Z = 4. The molecular structure and metrical data are similar to those of
the orthorhombic form, although the Pt · · · Pt separation is slightly less
◦
˚
˚
[3.361(1) A].
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Scheme 4
or 2 at room temperature. The colourless solids, 13 and 14, which
are formed in comparable amounts to 10 or 11, are insoluble in
common organic solvents. Unexpectedly, their IR spectra show no
bands in the region 2000–2100 cm−1 or 1700–1850 cm−1 typical of
terminal or acyl C–O stretching, respectively. Elemental analyses
were somewhat variable and suggest that a small amount of Cl,
presumably arising from CH2Cl2 that had been used in work-
up, was present. The composition of 14 seemed to correspond
approximately to the formula [Pt(C6H3-5-Me-2-PPh2)2]. That 13
and 14 are indeed isomers of 10 and 11, respectively, is indicated
by the observation that they are converted into 10 or 11 on heating
in toluene for 24 h.
The solid state 31P NMR spectrum of 14 consists of two
resonances of about the same intensity at d −61.0 and 19.0, each
flanked by 195Pt satellites (JPtP 1118 Hz and 2119 Hz, respectively).
The chemical shifts and coupling constants are similar to those of
10 and 11, which suggests that the disposition of ligand atoms in
14 is similar to that in 10 and 11. On this basis we assign 13 and
14 the structures shown, in which the bridging C6H3-5-R-2-PPh2
(R = H, Me) groups span platinum atoms in neighbouring units,
thus making an infinite chain polymer and accounting for the poor
solubility in organic solvents.
Fig. 2 Molecular structure of [Pt2(j2-2-C6H4PPh2)2(l-2-C6H4PPh2)2] 10.
Ellipsoids show 30% probability levels and hydrogen atoms have been
deleted for clarity. Asterisks indicate atoms generated by crystallo-
3
˚
graphic symmetry (1 − x,
− y, z). Selected bond lengths (A)
2
and angles (◦): Pt(1)–P(1) 2.321(1), Pt(1)–P(2) 2.297(1), Pt(1)–C(112)
2.070(5), Pt(1)–C(212*) 2.060(5), Pt(1) · · · Pt(1*) 3.3875(4), P(1)–Pt(1)–
P(2) 103.71(5), P(1)–Pt(1)–C(112) 68.8(1), P(1)–Pt(1)–C(212*) 157.7(1),
P(2)–Pt(1)–C(112) 166.4(2), P(2)–Pt(1)–C(212*) 92.7(1), C(112)–Pt(1)–
C(212*) 91.8(2).
Attempts to open the remaining chelate rings of 10 or 11 to form
a lantern-type dimer in which all four ortho-metallated ligands
bridge the two platinum atoms were unsuccessful. Complex 11
was recovered unchanged, with only a trace of decomposition,
even after 2 weeks in refluxing mesitylene or after UV-irradiation
for several hours. That a lantern structure can be generated by
heating the arsenic analogue of 1117 may be attributed to the
weaker Pt–As bonds, which allow facile dissociation and binding
to the neighbouring metal atom.
Heating a suspension of the 6-methyl compound cis-3 in toluene
gave only traces of the corresponding dimer 12, which was
identified by the appearance of two, equally intense multiplets in
the 31P NMR spectrum at d −64.9 and 22.4; the derived coupling
constants are similar to those in 10 and 11 (Table 1). The main
product was trans-[Pt(j2-C6H3-6-Me-2-PPh2)2], trans-3, which was
isolated as a poorly soluble, white solid in 62% yield. Its EI-mass
spectrum contains a parent ion peak at m/z 745, and the 31P NMR
spectrum shows a singlet at d −62.9 (JPtP 2445 Hz). The chemical
shift confirms that the four-membered rings have been retained
and the coupling constant is typical of P trans to P in planar Pt(II)
complexes.19
Complex cis-3 also reacts readily with CO at room temperature
and pressure but the product in this case is a mono-carbonyl com-
plex [Pt(CO)(jC-C6H3-6-Me-2-PPh2)(j2-C6H3-6-Me-2-PPh2)] 15,
which can be isolated in quantitative yield. The added CO is
lost slowly from the solid at room temperature, and more rapidly
in vacuo over a period of 24 h, to give trans-3, hence satisfactory
elemental analyses were not obtained. The structure can be
assigned unequivocally on the basis of spectroscopic data. There is
a parent-ion peak at m/z 773 in the EI-mass spectrum and a strong
m(CO) band at 2053 cm−1 in the IR spectrum, cf. 2050 cm−1 for cis-
[PtPh2(CO)(PPh3)] and 2048 cm−1 for cis-[PtPh2(CO)(PMePh2)].20
The 31P NMR spectrum consists of a pair of doublets at d −12.3
and −62.4 (JPP 2.2 Hz), each with Pt satellites (JPtP 179 Hz and
1130 Hz, respectively). The chemical shift and small JPtP for the first
resonance are characteristic of uncoordinated phosphorus in this
type of compound, cf. [Pt(L)(jC-2-C6H4PPh2)(j2-2-C6H4PPh2)]
We assume that the dimers 10 and 11 are formed by initial
dissociation of the phosphorus end of one of the chelate rings
of cis-1 or cis-2 and subsequent recombination of the two three-
coordinate fragments (Scheme 4). For cis-3, the first step is the
same, but the presence of the sterically hindering 6-methyl group
presumably favours cis → trans isomerisation over dimerisation.
Reactions with carbon monoxide
Exposure of solutions of 1 or 2 to CO (1–2 bar) at room
temperature causes an immediate colour change to yellow and the
formation of a white precipitate. From the solution, the dinuclear
complexes 10 or 11 can be isolated in ca. 40% yield; evidently CO
catalyses opening of one of the four-membered chelate rings of 1
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[L = PPh3, P(OPh)3, P(OMe)3, ButNC)];3 the second resonace
clearly belongs to bidentate j2-C6H3-6-Me-2-PPh2. The similarly
prepared 13CO adduct 15a shows a pair of bands due to m(CO)
in its IR spectrum at 2004 and 1996 cm−1 (presumably a solid
state splitting); the 31P NMR spectrum displays a doublet at d
−12.5 (unresolved JPP/JPC 1.9 Hz, JPtP 179 Hz) and a doublet of
Formation and reactions of diplatinum(I) complexes
Comproportionation of 1 or 2 with [Pt(PPh3)3] or [Pt(PPh3)2-
(C2H4)] in refluxing toluene gives, in 75–80% isolated yield, bright
yellow, microcrystalline diplatinum(I) complexes [Pt2(l-C6H3-5-
R-2-PPh2)2(PPh3)2] (R = H 16, Me 17) derived by opening of the
four-membered rings in 1 or 2. The X-ray structure and 31P NMR
spectrum of 16 were reported in a preliminary communication,2
and a more precise structural determination of 17 is described
below.
doublets at −62.5 (JPP 2.3 Hz, JPC 3.6 Hz, JPtP 1129 Hz). The 13
C
NMR spectrum also contains a doublet of doublets at d 176.6 (JPC
1.4, 3.6 Hz) due to 13CO flanked by 195Pt satellites (JPtC 1102 Hz).
The small values of JPtC and JPC are consistent only with a structure
for 15 in which CO is trans to the aryl carbon of the bidentate P–C
ligand.21–23
Attempted reaction of cis-3 with [Pt(PPh3)3] gave a complex
mixture and no 6-methyl analogue of 16 or 17 could be identified
in the 31P NMR spectrum. Attempts to generate a Pt–Pd analogue
of 17 by use of [Pd(PPh3)4] in place of [Pt(PPh3)3] also failed.
The MALDI-mass spectrum of 17 contains a peak at m/z
1465 corresponding to the [M + H]+ fragment and the 1H NMR
spectrum shows a single methyl resonance, indicating that the
bridging groups are in identical environments. The 31P NMR
spectrum consists of two 1 : 2 : 1 triplets (AAꢀBBꢀ pattern)
centred at d −3.0 and 26.3 due to l-C6H3-5-Me-2-PPh2 (PA)
and coordinated PPh3 (PB), respectively. Satellites arising from
isotopomers containing one and two 195Pt nuclei are also present.
The spectrum can be simulated to provide the P–P and Pt–P
coupling constants that are listed in Table 2, together with those
previously reported for 16.2 The parameters are similar both to
each other and to those of the structurally similar compound de-
rived from 1,2-bis(diphenylphosphino)ethane (dppe), viz., [Pt2{l-
C6H4P(Ph)CH2CH2PPh2}2].28 There is a minor difference in the
magnitude of 1JPtP for the phosphorus atom of the ortho-metallated
ring (1937 Hz for 16, 1918 Hz for 17), which can be attributed to
the electronic effect of the p-methyl substituent. The magnitude
of JPtP for P trans to C (1918 Hz) and P trans to Pt–Pt (1862 Hz)
indicate that the Pt–Pt bond has a similar trans-influence to that
of Pt–C(aryl).
These observations indicate that coordination of CO to plat-
inum, triggering dissociation of the phosphorus end of one of
the chelate ligands, is a plausible first step in the CO-catalysed
dimerisation and polymerisation of 1 and 2, as shown in Scheme 5.
The dangling phosphine can then coordinate to another platinum
centre, thus initiating dimerisation or polymerisation, with elimi-
nation of CO. In the reaction of cis-3 with CO, complex 15, which
models the intermediate carbonyl complex proposed in the cases
of cis-1 and cis-2, can be isolated, probably because the 6-methyl
groups block any intermolecular coordination of the displaced
phosphorus atom. It may seem surprising at first sight that CO
does not insert in the Pt–C r-bond in the first step, since this
would lead to a presumably less strained, five-membered chelate
acyl containing the ligand j2-P,C-COC6H3-5-R-2-PPh2 (R = H,
Me). This type of reaction occurs readily for ortho-metallated PPh3
complexes of Mn(I),24 Ru(II),25 Co(I)26 and Rh(I).27 In the first step,
however, CO is presumably located trans to the aryl carbon atom
of the bidentate P–C ligand, as found for 15, and therefore cannot
undergo cis-insertion into the aryl carbon–metal bond of the four-
membered ring.23
The molecular structure of 17 determined by single-crystal
X-ray diffraction analysis is shown in Fig. 3, together with
significant metrical data. A pair of platinum atoms is coordinated
by two bridging C6H3-5-Me-2-PPh2 groups and two axial PPh3
ligands, each platinum atom being in a distorted square planar
coordination environment. The Ph3P–Pt–Pt–PPh3 unit is close
Table 2 31P NMR parameters for [Pt2(l-C6H3-5-R-2-PPh2)(PPh3)2] (R =
H 16, Me 17) and [Pt2(l-Y)(l-C6H3-5-R-2-PPh2)(PPh3)2]+ (Y = I, R = H
[19]+, Me [20]+; Y = H, R = H [22]+)a,b
16
17
[19]+
[20]+
[22]+
d(PA)
d(PB)
−3.6
−3.0
5.6
15.5
1677
5065
29
0
5.0
16.1
1674
5080
30
0
3.1
22.9
1704
3701
48
24.1
26.3
J(AX)
J(BX)
J(AAꢀ)
J(BBꢀ)
J(AXꢀ)
J(BXꢀ)
J(AB)
J(ABꢀ)
1937
1866
55
226
−140
1149
10
1918
1862
56
228
−140
1160
11
66
0
0
−50
387
18
123
20
0
123
20
0
10
11
0
a Labelling of nuclei: B(A)X–Xꢀ(Aꢀ)Bꢀ, where PA, PA are the 31P nuclei in
ꢀ
the bridging ortho-metallated ring, PB, PB are the 31P nuclei of the PPh3
ꢀ
ligands, and X = 195Pt. Note that the labelling of X, Xꢀ is reversed from
that used in ref. 2. J(XXꢀ) could not be determined. b 16 and 17 measured
in C6D6, 19, 20 and 22 in CD2Cl2.
Scheme 5
3162 | Dalton Trans., 2007, 3158–3169
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Table 3 31P NMR parameters for [Pt2(l-2-C6H4PPh2)2(CNBut)2] 18 and
[Pt2(l-H)(l-2-C6H4PPh2)(CNBut)2]+ 21+a
18
21+
d
−4.2b
6.2c
1514
58
J(AX)
J(AAꢀ)
J(AXꢀ)
J(XXꢀ)
1920
64
−137
−74
4421
2711
a Labelling of nuclei: AX · · · AꢀXꢀ, where A, Aꢀ are the 31P nuclei in the
bridging ortho-metallated ring and X = 195Pt. b In C6D6. c In CD2Cl2.
2022 cm−1 and is probably the mono-carbonyl. In other solvents
products having more complex spectra are obtained, which have
not been investigated further.
Fig. 3 Molecular structure of [Pt2(l-C6H3-5-Me-2-PPh2)2(PPh3)2] 17.
Ellipsoids show 30% probability levels and hydrogen atoms have
Treatment of complexes 16 and 17 with one equivalent of
iodine in CH2Cl2 gives the orange, A-frame diplatinum(II) com-
plexes [Pt2(l-I)(l-C6H3-R-2-PPh2)2(PPh3)2]I (R = H [19]I; R =
Me [20]I). The X-ray structure and NMR data for [19]I were
reported previously.2 The MALDI-mass spectrum of [20]+ shows
the expected [M + H]+ peak at m/z 1592 and the 1H NMR
spectrum shows a single methyl resonance at d 1.53, confirming
that the bridging C6H3-5-Me-2-PPh2 groups are in equivalent
environments. The 31P NMR spectrum of [20]+, like that of [19]+,
shows two main resonances, as approximately 1 : 1 : 1 : 1 quartets,
at d 5.0 and 16.1, for the l-C6H3-5-Me-2-PPh2 (PA) and PPh3 (PB)
ligands, respectively, with sub-spectra arising from P–P and Pt–P
coupling. The derived coupling constants are listed in Table 2.
Disruption of the Pt–Pt interaction in 16 and 17 by iodine is
indicated by the reduction of the P–P coupling between the PPh3
ligands from ca. 230 Hz to zero, and by the reduction of the
◦
˚
been deleted for clarity. Selected bond lengths (A) and angles ( ):
Pt(1)–Pt(2) 2.61762(16), Pt(1)–P(1) 2.3014(8), Pt(1)–P(3) 2.29505(8),
Pt(1)–C(212) 2.045(3), P(1)–Pt(1)–C(212) 163.39(9), Pt(2)–Pt(1)–P(3)
173.12(2), P(1)–Pt(1)–P(3) 102.73(3), Pt(2)–Pt(1)–C(212) 85.61(8).
˚
to linear. The Pt–Pt distance [2.61762(16) A] is similar to
2
˚
that of 16 [2.630(1) A] and [Pt2{l-C6H4P(Ph)CH2CH2PPh2}2]
[2.628(1) A],28 and is consistent with the presence of a direct Pt(I)–
˚
Pt(I) (5d9–5d9) bond. The similar Pt–P bond lengths for l-C6H3-5-
˚
˚
˚
Me-2-PPh2 [2.3014(8) A] and PPh3 [2.2905(8) A] can be compared
with that found in cis-[PtCl2(PPh3)2] [2.264(7) A];29 they reflect the
high trans-influence of the Pt–C(aryl) and Pt–Pt bonds inferred
from the 31P NMR data.
In light of the chemistry already described, it seems plausible
that 16 and 17 are formed by coordination of dangling phosphorus
atoms arising from opening of the four-membered rings of 1 and
2 to a Pt(PPh3)2 fragment generated by dissociation of L from
[Pt(PPh3)2(L)] (L = PPh3, C2H4).
ꢀ
indirect Pt–PPh3 coupling (JBX ) from 1160 Hz to 123 Hz. The
large increase in the direct coupling (JBX) from ca. 1870 Hz in 16
and 17 to more than 5000 Hz in [19]+ and [20]+ is consistent with
P trans to halide; the remarkably high value appears also to be
characteristic of halide cis to an aryl or aroyl group in binuclear
platinum(II) complexes.33
The axial PPh3 ligands of 16 are replaced rapidly by t-butyl
isocyanide at room temperature to give the diplatinum(I) complex
[Pt2(l-2-C6H4PPh2)2(CNBut)2] 18 as a pale yellow solid. It shows
a m(C≡N) band at 2125 cm−1 in the IR spectrum and resonances
typical of ButNC in its 1H and 13C NMR spectra. The 31P NMR
spectrum contains only a singlet in the region of d −4 due to
equivalent 2-C6H4PPh2 ligands accompanied by satellite peaks
due to the mono-195Pt and bis-195Pt isotopomers. Analysis of the
AAꢀX and AAꢀXXꢀ sub-spectra30 yields the parameters shown in
Treatment of complex 16 with an excess of HCl cleaves both the
Pt–Pt and Pt–C bonds giving cis-[PtCl2(PPh3)2], but strong acids
containing poorly coordinating anions react with 16–18 forming
l-hydridodiplatinum(II) cations having an A-frame structure,
1
which are readily identified by H and 31P NMR spectroscopy.
1
Thus, complex 18 reacts with HBF4 to give the colourless salt
[Pt2(l-H)(l-2-C6H4PPh2)2(CNBut)2]BF4 [21]BF4, whose hydride
resonance appears at d −8.7 as the expected 1 : 8 : 18 : 8 : 1 quintet
of triplets arising from coupling with a pair of equivalent platinum
atoms and a pair of phosphorus nuclei (JPtH 760 Hz, JPH 7 Hz).
The Pt–Pt coupling constant derived from the 31P NMR spectrum
of [21]+, ca. 2700 Hz, is less than that in its precursor 18 (Table 3),
consistent with a weakening of the Pt–Pt bond by protonation.
Complex 16 is protonated similarly by HBF4, HPF6, CF3CO2H,
CF3SO3H or p-tolSO3H to give colourless salts of the cation [Pt2(l-
H)(l-2-C6H4PPh2)2(PPh3)2]+ [22]+. The 1H NMR spectrum of the
cation shows a hydride resonace at d −5.17 in which the inner three
resonances of the 1 : 8 : 18 : 8 : 1 quintet of triplets are split further
into 1 : 2 : 1 triplets owing to strong coupling with the 31P nuclei
of the two PPh3 ligands that are trans to hydride (JPH 80 Hz); the
outer resonances were not detected. The chemical shift and Pt–
H coupling constant (735 Hz) are similar to those observed for
Table 3; the derived value of 4421 Hz for JPtPt suggests that a
metal–metal bond is present, although there is a wide variation in
the magnitude of this coupling constant even in compounds that
are known to contain Pt–Pt bonds.30–32
Carbon monoxide also displaces PPh3 from 16 at room temper-
ature but the products are stable in solution only under CO. The
first-formed compound, which precipitates to some extent when
the reaction is done in hexane, shows a strong m(CO) band at
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◦
˚
the bridging hydride in [Pt2H2(l-H)(l-dppm)2]PF6 (d −5.86, JPtH
540 Hz).34 No band assignable to m(PtH) could be detected in the
IR spectra of [21]+ or [22]+.
Table 4 Selected bond distances (A) and angles ( ) in [Pt2(l-H)(l-C6H3-
5-Me-2-PPh2)2(PPh3)2]PF6·H2O·0.48Et2O [23]PF6
Pt(1)–P(1)
Pt(2)–P(2)
Pt(1)–C(212)
2.3424(14) Pt(1)–P(3)
2.3602(13) Pt(2)–P(4)
2.3099(15)
2.2958(13)
2.082(4)
The Pt–P and P–P coupling constants derived from analysis
of the 31P NMR spectrum of [22]+ are given in Table 2. Notable
is the magnitude of JPtP, 3701 Hz, to the phosphorus atoms of
the PPh3 ligands, which are trans to the bridging hydride in an
ideal A-frame structure, cf. the unexpectedly large values of the
same coupling constants trans to bridging iodide in [19]+ and
[20]+ (see above). In mononuclear Pt(II) complexes a JPtP value
of 3701 Hz would imply that the phosphorus atom was trans
2.071(5)
Pt(2)–C(112)
Pt(1) · · · Pt(2)
Pt(2)–Pt(1)–P(3)
P(1)–Pt(1)–P(3)
Pt(2)–Pt(1)–C(212)
Pt(1)–Pt(2)–P(2)
Pt(1)–Pt(2)–H(1)
2.7888(3)
161.32(4)
100.52(5)
91.03(14)
77.06(3)
30.4(4)
Pt(1)–H(1)
1.62(1)
Pt(1)–Pt(2)–P(4)
P(2)–Pt(2)–P(4)
Pt(1)–Pt(2)–C(112)
Pt(2)–Pt(1)–H(1)
164.64(3)
101.04(5)
91.89(14)
30.5(4)
to a strongly electron-withdrawing or weakly bonded ligand.19
A
similar observation has been made in the case of the (l-hydrido)(l-
diphenylphosphido)diplatinum(II) cation [(PPh3)(Ph)Pt(l-H)(l-
PPh2)Pt(PPh3)2]+, for which JPtP(PPh3) trans to hydride is
3785 Hz.35,36 The relatively low trans-influence of bridging hydride
has been noted in other dinuclear platinum(II) complexes.34–37
Treatment of [22]+ with aqueous K2CO3 at 40 ◦C or NH3 at
room temperature re-forms 16 quantitatively. The reaction with
BunLi is more complicated. Only ca. half the expected quantity of
16 is formed, together with approximately equal amounts of two
other compounds that have not been separated or identified.
The corresponding salt [Pt2(l-H)(l-C6H3-5-Me-2-PPh2)2-
(PPh3)2]PF6 [23]PF6 obtained from 17 and HPF6 shows a peak
in its MALDI-mass spectrum at m/z 1465 corresponding to [M −
PF6]+ and a hydride resonance at d −5.22 (JPtH 735 Hz) in the
1H NMR spectrum similar in multiplicity to that of [22]+, though
less well resolved. Unexpectedly, however, there are three aromatic
methyl resonances of equal intensity, suggesting that [23]PF6 may
not be a single compound. The 31P NMR spectrum resembles that
of [22]+ in its general features: there are two multiplets of equal
intensity at ca. d 23.5 and 3 due to PPh3 and the ortho-metallated
ligand, respectively, the former showing two pairs of 195Pt satellites
(JPtP ca. 3900, 400 Hz) and the latter one pair (JPtP ca. 1700 Hz).
However, the spectrum of [23]+ is more complex than that of [22]+
and simulation was not attempted.
Fig. 4 Molecular structure of the cation of [Pt2(l-H)(l-C6H3-5-Me-
2-PPh2)2(PPh3)2]PF6·H2O·0.48Et2O [23]PF6. Ellipsoids show 30% prob-
ability levels. Hydrogen atoms, with the exception of the bridging hydride,
have been deleted for clarity.
The process responsible for the scrambling is probably reversible
C–H reductive elimination and oxidative addition, as shown
in Scheme 6. The l-hydride in [23]+ can undergo reductive
elimination with one of the bridging p-tolyl groups forming
coordinated 4-tolyldiphenylphosphine, and leaving one bridging
ortho-metallated group. The reverse process of C–H oxidative
addition that regenerates l-hydride can then occur either from
The X-ray structure of the cation in [23]PF6 is shown in Fig. 4;
selected bond lengths and angles are collected in Table 4. The
geometry of the cation is similar to that of the l-iodo cation in
[19]I. The hydride ligand H(1), which was located in the difference
electron-density map, occupies the apical position. The cation is
disordered in such a way that the phosphine ligand containing
P(1) is ortho-metallated to Pt(2) to the extent of 75% via the
p-tolyl group and 25% via a P–Ph group of the bridging unit.
Correspondingly, the phosphine ligand containing P(2) is ortho-
metallated to Pt(1) to the extent of 30% via the p-tolyl group
and 70% via a P–Ph group. This scrambling of p-methyl groups
between the aryl groups of the ortho-metallated unit accounts
1
for the appearance of several H aromatic methyl resonances in
solution arising from closely related, isomeric species.
Scheme 6
3164 | Dalton Trans., 2007, 3158–3169
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a 4-tolyl or a phenyl group of 4-tolyldiphenylphosphine, giving, in
the latter case, bridging 2-C6H4P(Ph)(C6H4-p-Me). The process
can be repeated with the second bridging C6H3-5-Me-2-PPh2
ligand. Reductive elimination of benzene and alkanes, respectively,
from mononuclear cis-hydrido(phenyl)- and cis-hydrido(alkyl)-
platinum(II) complexes, cis-[PtH(R)(PPh3)2], occurs readily, but,
in contrast with the behaviour reported here, these processes are
irreversible.38
is about twice its value in mononuclear Pt(II) hydrides having
hydride trans to PR3 (e.g. 1984 Hz in cis-[PtH2(PEt3)2]).48 A similar
explanation has been advanced to account for the magnitude of
JPtP (2741 Hz) in the cis-[PtH2(PEt3)2] moiety of cis-[(Et3P)2Pt(l-
H)2PtH(PEt3)2]+.37
Conclusions
The Pt–Pt separation in [23]PF6 [2.7888(3) A] is greater than that
The bis(chelate) complexes cis-[Pt(j2-C6H3-5-R-2-PPh2)2] (R = H
1, Me 2) are not thermodynamically stable and are converted on
heating, or on treatment with CO, into dimers containing bridging
and chelating ligands, [Pt2(j2-C6H3-5-R-2-PPh2)2(l-C6H3-5-R-2-
PPh2)2] (R = H 10, Me 11). In contrast with the analogous tertiary
arsine system, these dimers do not isomerise further to complexes
containing four bridging carbanionic ligands. Dimer formation
probably proceeds by initial dissociation of the phosphorus end of
the chelate ring. The presence of a 6-methyl substituent sterically
inhibits dimer formation, so that cis-[Pt(j2-C6H3-6-Me-2-PPh2)2],
cis-3, preferentially isomerises to trans-3 on heating, and reacts
with CO to give a platinum(II) carbonyl complex 15 containing
C6H3-6-Me-2-PPh2 behaving unusually as a monodentate, C-
bonded ligand. Likewise, comproportionation of 1 and 2 with
[Pt(PPh3)2L] (L = PPh3, C2H4) to give the metal–metal bonded,
diplatinum(I) complexes 16 and 17 occurs cleanly for 2-C6H4PPh2
and C6H3-5-Me-2-PPh2, whereas the attempted formation of a
diplatinum(I) complex from 3 by a similar route failed. Although
the 5-methyl substituent in the carbanion makes little difference to
the chemistry of platinum(II) and diplatinum(I), its presence helps
to establish the occurrence of a reversible reductive elimination–
oxidative addition sequence between hydride and the metal–aryl
bonds of the bridging carbanion in [23]+. Reductive elimination
and oxidative addition reactions involving hydride and methyl lig-
ands are a well-established feature of the diplatinum(I) chemistry
of l-bis(diphenylphosphino)methane and related ligands.49
˚
˚
in 17 [2.61762(16) A], demonstrating the expected lengthening,
and presumably weakening, of the metal–metal bond in the
latter on protonation. The corresponding separation in the l-
+
˚
iodo cation [19] , 2.931(2) A, is even greater, probably because
of the larger bridging ligand. The Pt–Pt separation in [23]PF6 is
also significantly less than in mono-l-hydrido complexes, such
as trans-YL2Pt(l-H)PtYꢀL2]+ (Y = Yꢀ = H, L = PEt3; Y = H,
Yꢀ = Ph, L = PEt3; Y = Yꢀ = Ph, L = PMe3, PEt3; Y = Yꢀ =
C6F5, L = PMe3), whose Pt–Pt distances are in the range 3.00–
39–42
˚
3.25 A.
However, mono-l-hydridodiplatinum(II) complexes
that contain another bridging group, such as l-PPh2, l-S or l-
C≡CR, or complexes that have cis-bidentate instead of trans-
tertiary phosphines, have Pt–Pt separations that are similar to
43
˚
that in [23]PF6, e.g., [Pt2(l-H)(l-CO)(dppe)2]BF4 [2.716(1) A],
44
˚
[Pt2(l-H)(l-S)(dppe)2]BF4 [2.774(1) A], [(Ph)(Ph3P)Pt(l-H)(l-
˚
PPh2)Pt(PPh3)2]Y [Y = BF4, 2.889(2), 2.912(2) A, independent
35,36
˚
molecules; Y = CH(SO2CF3)2, 2.885(1) A],
[Pt2(l-H)(l-
45
˚
C≡CPh)(C6F5)2(PPh3)2] [2.8159(10) A], and [Pt2H2(l-H)(L–
46
˚
L)]BF4 [L–L = EtN(PPh2)CHEtCH2OPPh2, 2.736(1) A]. Thus,
the three-centre Pt–H–Pt interaction in [23]PF6 appears to be
“closed” and to retain some Pt–Pt bonding. The Pt–H distances,
which were restrained to be equal in the positional refinement,
˚
were found to be 1.62(1) A and the angle subtended at the
hydride about 119(1)◦. These parameters are comparable with
those cited for other mono-l-hydridodiplatinum(II) complexes,
˚
e.g. trans-[R(Me3P)2Pt(l-H)PtR(PMe3)2]BPh4 [1.79(8), 1.73(7) A,
121(5)◦ for R = Ph; 1.6(1), 1.7(1) A, 126(9) for R = C6F5].42
The P(3)–Pt(1)–Pt(2) and P(4)–Pt(2)–Pt(1) angles [161.32(4)◦ and
164.64(3)◦, respectively] are smaller than those observed in 17
owing to the presence of the bridging hydride.
◦
˚
Experimental
All experiments were carried out in an inert atmosphere with use
of standard Schlenk techniques, though the platinum complexes
were stable to air once isolated. Solvents were dried and degassed
by standard procedures. Triflic acid was distilled before use;
all other materials were used without further purification. The
The Pt–P distances to the ortho-metallated ligands of [23]PF6
[2.3424(14), 2.3602(13) A] are significantly greater than those in
˚
˚
17 [2.3014(8), 2.3030(8) A], reflecting the trend in Pt–P coupling
constants of 17 and [22]+ (Table 2). On the other hand, the Pt–PPh3
NMR spectra were measured on Jeol FX 200 (13C 50.3 MHz, 31
P
˚
distances in 17 and [23]PF6 are unexceptional (ca. 2.30 A) and do
81.0 MHz), Varian Gemini 2000 (13C 50.3 MHz), Varian XL-
200 (31P 81.0 MHz) and Bruker Aspect 2000 (1H 300 MHz,
31P 121.0 MHz) instruments. The 1H and 13C chemical shifts
(d) were measured relative to the residual signals of CD2Cl2
(dH 5.32, dC 52.6), C6D6 (dH 7.15, dC 128.0) or CDCl3 (dH 7.26,
dC 77.0); 31P NMR spectra were recorded with 85% H3PO4 as
external reference. Spectral simulations were carried out on an in-
house program at the University of Victoria, British Columbia,
Canada or by use of the gNMR program.50 Infrared spectra were
measured as KBr discs on Perkin Elmer 683 grating, Spectrum
2000 FT or 1800 instruments. Solid state 31P NMR spectra at
121 MHz were obtained on a Varian Inova 300 instrument using
a 4 mm Chemagnetics cross-polarisation, magic angle spinning
(CP-MAS) probe. The samples were contained in 4 mm rotors
made of partially stabilised zirconia. The spectra were acquired at
a spinning speed of 13 kHz with a 120 s delay between pulses and
not differ significantly, even though the magnitude of JPtP(PPh3)
(3701 Hz) in the latter is about twice that in the former (see above
and Table 2). This situation differs from that in [Ph(Ph3P)Pt(l-
H)(l-PPh2)Pt(PPh3)2]+, in which the Pt–P(PPh3) distance trans
35
˚
˚
to the bridging hydride is significantly shorter [2.270(8) A,
36
˚
2.274(3) A ] than the other Pt–P(PPh3) distances (2.32–2.33 A),
corresponding to the unexpectedly large Pt–P coupling constant
(3785 Hz). Venanzi et al.35 suggested that this might indicate the
hydride in the l-PPh2 cation (which was not located directly) to
be bridging unsymmetrically between the two platinum atoms,
but this clearly cannot apply to [23]PF6. Perhaps the simplest
explanation for the large Pt–P coupling constant trans to l-hydride
in [23]+ is that the high demand for Pt 6s-electron density made by
hydride can be shared equally between the two platinum atoms,
hence the Pt–P coupling constant, which reflects this demand,47
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Table 5 Elemental analyses of platinum complexesa
% C
% H
% P
cis-[Pt(j2-C6H3-5-Me-2-PPh2)2] cis-2
60.85 (61.21)
61.08 (61.21)
61.28 (61.21)
55.97 (55.89)
45.75 (45.66)
52.38 (52.77)
59.90 (60.24)
59.90 (61.21)
57.40 (61.21)
59.82 (60.16)
60.49 (60.65)
51.43 (51.20)
56.43 (56.70)
54.49 (55.24)
58.42 (58.95)
55.04 (55.16)
4.43 (4.33)
4.25 (4.33)
4.11 (4.33)
3.98 (3.95)
3.46 (3.23)
4.17 (3.97)
4.20 (3.90)
4.36 (4.33)
3.91 (4.33)
4.09 (4.07)
4.38 (4.26)
4.41 (4.30)
3.88 (3.90)
3.64 (3.75)
4.05 (4.13)
3.82 (3.94)
8.25 (8.31)
8.43 (8.31)
8.29 (8.31)
7.78 (7.59)b
6.20 (6.20)
7.05 (6.98)
8.22 (8.65)
8.36 (8.31)
8.35 (8.31)c
8.39 (8.63)
8.76 (8.45)
5.48 (5.74)d
8.37 (8.12)
7.79 (7.80)e
7.62 (7.70)
9.92 (9.61)
cis-[Pt(j2-C6H3-6-Me-2-PPh2)2] cis-3
trans-[Pt(j2-C6H3-6-Me-2-PPh2)2] trans-3
trans,cis,cis-[PtCl2(j2-C6H3-5-Me-2-PPh2)2] 4
cis,cis,cis-[PtI2(j2-C6H3-5-Me-2-PPh2)2] 6
trans,cis,cis-[PtI(Me)(j2-C6H3-5-Me-2-PPh2)2] 7
[Pt2(j2-2-C6H4PPh2)2(l-2-C6H4PPh2)2] 10
[Pt2(j2-C6H3-5-Me-2-PPh2)2(l-C6H3-5-Me-2-PPh2)2] 11
[Pt2(j2-C6H3-5-Me-2-PPh2)2(l-C6H3-5-Me-2-PPh2)2]n 14
[Pt2(l-2-C6H4PPh2)2(PPh3)2] 16
[Pt2(l-C6H3-5-Me-2-PPh2)2(PPh3)2] 17
[Pt2(l-2-C6H4PPh2)2(CNBut)2] 18
[Pt2(l-H)(l-2-C6H4PPh2)2(PPh3)2]BF4 [22]BF4
[Pt2(l-H)(l-2-C6H4PPh2)2(PPh3)2]CF3SO3 [22]OTf
[Pt2(l-H)(l-2-C6H4PPh2)2(PPh3)2][MeC6H4SO3] [22][p-Tos]
[Pt2(l-H)(l-C6H3-5-Me-2-PPh2)2(PPh3)2]PF6 [23]PF6
a Calculated values in parentheses. b % Cl 8.65 (8.68). c % Cl 0.62. d % N 2.50 (2.60). e % F 3.38 (3.59);% S 1.93 (2.02).
were referenced to external solid NH4(H2PO4) (d 1.0). Mass spectra
were measured on the following instruments: VG ZAB-2 SEQ
(FAB using 2-nitrophenyl octyl ether as matrix), HP 5970 MSD
(EI), and Bruker Biflex II (MALDI). Elemental analyses were
carried out at the Microanalytical Unit of the Research School of
Chemistry (ANU) and are listed in Table 5.
(CDCl3) d 2.07 (s, 6H, Me), 6.8–8.0 (m, 26H, aromatics); 31P NMR
(CDCl3) d −62.9 (s, JPtP 2445 Hz); EI-MS (m/z) 745 [M]+.
The compound [Pt2(j2-C6H3-6-Me-2-PPh2)2(l-C6H3-6-Me-2-
PPh2)2] 12 was observed in situ by 31P NMR spectroscopy but
it was contaminated with decomposition products and could not
be isolated. Its 31P NMR parameters are given in Table 2.
The compounds 2-BrC6H4PPh2,51 2-Br-4-MeC6H3PPh2,7 2-Br-
3-MeC6H3PPh2,7 [PtCl2(SEt2)2],52 PhICl2,53 [Pt(PPh3)n] (n = 3,
[PtXY(j2-C6H3-5-Me-2-PPh2)2] (X = Y = Cl 4, Br 5, I 6; X =
Me, Y = I 7). To a solution of cis-2 (100 mg, 0.134 mmol) in
CH2Cl2 (6 mL) was added PhICl2, Br2 or I2 (1 equiv.) in CH2Cl2
(6 mL), or neat methyl iodide (1 mL) at room temperature. The
solutions were stirred for 30 min, evaporated to dryness, and the
residues recrystallised from CH2Cl2–methanol. Yields were 80–
85%.
2
4),54 and [Pt(PPh3)2(g -C2H4)]55 were prepared by the appropriate
literature procedures.
Preparations
cis-[Pt(j2-C6H3-5-Me-2-PPh2)2], cis-2. This was prepared
from (2-Br-4-MeC6H3)PPh2 (1.143 g, 3.21 mmol), BunLi (2.1 mL
of 1.6 M solution in hexanes, 3.36 mmol) and [PtCl2(SEt2)2]
(0.638 g, 1.42 mmol) as described for cis-1.3 After recrystallisation
from CH2Cl2–methanol, cis-2 was obtained as a white solid
1
trans,cis,cis-4. Pale yellow solid; H NMR (CDCl3) d 2.47 (s,
6H, Me), 7.0–8.0 (m, 26H, aromatics); 31P NMR (CDCl3) d −67.7
(s, JPtP 928 Hz); EI-MS (m/z) 779 [M − Cl]+.
trans,cis,cis-5. Pale orange solid, not isolated in a pure state;
31P NMR (CDCl3) d −74.3 (s, Pt satellites not observed) due
to trans,cis,cis-5, −76.3 (d, JPP 5.9 Hz, JPtP 2081 Hz), −79.7 (d,
JPP 5.9 Hz, JPtP 965 Hz) due to cis,cis,cis-5. Product contami-
nated with [PtBr2(j2-C6H3-5-Me-2-PPh2){j2-O,C-C6H3-5-Me-2-
1
(0.868 g, 82%). H NMR (CDCl3) d 2.37 (s, 6H, Me), 6.8–7.8
(m, 24H, aromatics), 8.0 (t with br 195Pt satellites, JHH 4.7 Hz, JPH
4.7 Hz, JPtH 55.7 Hz, 2H, ortho-H); 31P NMR (CDCl3) d −52.2 (s,
JPtP 1352 Hz); IR (KBr, cm−1) 3043 m, 2910 m (C–H str), 1565 m
+
=
(arom C C str), 724 s (C–H def); EI-MS (m/z) 745 [M] . X-Ray
quality crystals were grown from CH2Cl2–methanol.
P(O)Ph2}], 62.9 (s, JPtP 64.6 Hz), −65.6 (s, JPtP 2119 Hz); IR
−1
=
(KBr, cm ) 3039 m, 2953 m (C–H str), 1561 m (arom C C str),
+
=
cis-[Pt(j2-C6H3-6-Me-2-PPh2)2], cis-3. This was prepared sim-
ilarly to cis-2 from (2-Br-3-MeC6H3)PPh2 (1.32 g, 3.72 mmol),
BunLi (1.6 M in hexanes, 2.5 mL, 4.00 mmol) and [PtCl2(SEt2)2]
(0.696 g, 1.56 mmol). The yield of cis-3, a white solid, was 0.616 g
1064 s (P O str), 724 s (C–H def); EI-MS (m/z) 823 [M − Br] ,
842 [M + O–Br]+.
cis,cis,cis-6. Orange solid; 1H NMR (CDCl3) d 1.88 (s, 3H, Me),
2.47 (s, 3H, Me), 6.0–8.2 (m, 26H, aromatics); 31P NMR (CDCl3)
d −94.0 (d, JPP 7.5 Hz, JPtP 928 Hz), −98.1 (d, JPP 7.5 Hz, JPtP
991 Hz); EI-MS (m/z) 872 [M − I]+.
1
(53%). H NMR (CDCl3) d 2.47 (s, 6H, Me), 6.8–8.0 (m, 26H,
aromatics); 31P NMR (CDCl3) d −62.9 (s, JPtP 1370 Hz); IR
1
−1
=
trans,cis,cis-7. Pale yellow solid; H NMR (CDCl3) d 0.92 (t,
(KBr, cm ) 3049 m, 2896 m (C–H str), 1562 m (arom C C str),
724 s (C–H def); EI-MS (m/z) 745 [M]+. X-Ray quality crystals
JPH 7.5 Hz, JPtH 70.9 Hz, 3H, PtMe), 2.41 (s, 6H, Me), 6.8–8.0
(m, 26H, aromatics); 31P NMR (CDCl3) d −75.7 (s, JPtP 936 Hz);
EI-MS (m/z) 887 [M]+, 760 [M − I]+.
[PtCl2(j2-C6H3-6-Me-2-PPh2)2] 8. To a solution of cis-3
(100 mg, 0.134 mmol) in CH2Cl2 (100 mL) was added PhICl2
(37 mg, 0.135 mmol) in CH2Cl2 (5 mL) and the solution was stirred
for 1 min. The solvent was evaporated to a small volume and
hexane was added. The resulting pale yellow solid was separated
were grown from CH2Cl2–pentane.
trans-[Pt(j2-C6H3-6-Me-2-PPh2)2], trans-3. A suspension of
cis-3 (180 mg, 0.241 mmol) in toluene (20 mL) was heated under
reflux for 48 h, during which time the solution became orange. The
solution was allowed to cool to room temperature. The resulting
white solid was separated by filtration, washed with toluene and
pentane and dried in vacuo to give trans-3 (112 mg, 62%). 1H NMR
3166 | Dalton Trans., 2007, 3158–3169
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by filtration, washed with hexane, and dried in vacuo. The yield
of 8 was 99 mg (90%) and the ratio of cis- to trans-adducts was
typically ca. 2 : 1. 31P NMR (CDCl3) d −76.9 (s, JPtP 958 Hz) (trans-
8), −76.2 (d, JPP 13.3 Hz, JPtP 2156 Hz) (cis-8); EI-MS (m/z) 779
[M − Cl]+.
trans,cis,cis-[PtI(Me)(j2-C6H3-6-Me-2-PPh2)2] 9. A solution
of cis-3 (2 mg, 0.003 mmol) in CD2Cl2 (0.7 mL) in an NMR tube
was treated with methyl iodide (0.2 mL). The mixture was shaken
thoroughly and its 31P NMR spectrum monitored periodically.
After 1 h the trans-adduct could be detected, together with starting
material, but there was extensive decomposition to unidentified
products. 31P NMR (CD2Cl2) d −83.9 (s, JPtP 955 Hz) (trans-9).
[Pt2(j2-2-C6H4PPh2)2(l-2-C6H4PPh2)2] 10. A solution of cis-
1 (358.5 mg, 0.50 mmol) in toluene (50 mL) was stirred for
24 h at a bath temperature of 130 ◦C. The solid had dissolved
completely at 80 ◦C and the colour of the solution slowly changed
to yellow. The course of the reaction was monitored by 31P NMR
spectroscopy and after 24 h less than 5% of cis-3 remained. The
solution was concentrated in vacuo to ca. 2 mL, transferred to a
silica gel column (length 20 cm, internal diameter 3.5 cm), and
eluted with toluene–hexane (10 : 1). The first yellow fraction, on
evaporation in vacuo, gave pure 10 (220 mg, 61%) as a pale yellow
powder, mp 286–288 ◦C, that is soluble in aromatic solvents, THF,
ether chloroform and dichloromethane. Solutions in chlorinated
solvents slowly decomposed.
The 13CO-labelled complex 15a was prepared similarly. 13C
NMR (CD2Cl2) d 22.3, 27.3 (Me), 125–140 (aromatics), 176.6 (dd,
JPC 1.4, 3.6 Hz, JPtC 1102, C≡O); 31P NMR (CD2Cl2) d −12.5 (br
d, J 1.9 Hz due to unresolved JPP and JPC, JPtP 179 Hz, uncoord.
P), −62.5 (dd, JPP 2.3 Hz, JPC 3.6 Hz, JPtP 1129 Hz, coord. P); IR
(KBr, cm−1) 2004, 1996 (13C≡O str).
[Pt2(l-2-C6H4PPh2)2(PPh3)2] 16. A solution containing cis-1
(150 mg, 0.21 mmol) and [Pt(PPh3)3] (206 mg, 0.21 mmol) in
toluene (20 mL) was stirred for 24 h at 130 ◦C (bath temperature).
The colour changed from orange to red–brown. The solution was
concentrated in vacuo to ca. half-volume and ethanol was added.
The precipitated, bright yellow solid was separated by filtration,
washed with ethanol (3 × 30 mL), and dried in vacuo to give 231 mg
(77%) of 16, mp 210–214 ◦C (dec.). The air-stable yellow powder
is soluble in aromatic and chlorinated solvents, and in acetone; the
solutions in chlorinated solvents decompose slowly.
[Pt2(l-C6H3-5-Me-2-PPh2)2(PPh3)2] 17. This was prepared
similarly to 16 from cis-2 (232 mg, 0.31 mmol) and [Pt(PPh3)3]
(305 mg, 0.31 mmol) in toluene (30 mL). The product was
recrystallised from CH2Cl2–methanol to give 17 as a bright yellow
solid (342 mg, 75%). 1H NMR (C6D6) d 1.73 (s, 6H, Me), 6.4–7.5
(m, 56H, aromatics); MALDI-MS (m/z) 1465 [M + H]+. Crystals
suitable for X-ray diffraction were obtained from CH2Cl2–ether.
The reaction time can be shortened to 30 min if
[Pt(PPh3)2(C2H4)] is used in place of [Pt(PPh3)3]. Yields are
typically 80%.
[Pt2(j2-C6H3-5-Me-2-PPh2)2(l-C6H3-5-Me-2-PPh2)2] 11. (a)
A colourless solution of cis-2 (150 mg, 0.201 mmol) in toluene
(30 mL) was heated under reflux for 48 h, during which time a
yellow colour developed. The solution was evaporated in vacuo,
ethanol was added, and the yellow precipitate was separated by
filtration, washed with ethanol, and dried in vacuo. The yield of 11
was 116 mg (77%). 1H NMR (C6D6) d 1.80 (s, 6H, Me), 1.84 (s, 6H,
Me), 6.4–7.2 (m, 44H, aromatics), 7.94 (dd, J 7.0, 10.5 Hz, 4H,
aromatics), 8.14 (dd, J 7.7, 9.9 Hz, 4H, aromatics); MALDI-MS
(m/z) 1491 [M]+.
(b) A benzene solution of cis-2 (150 mg, 0.201 mmol) was stirred
for 48 h under CO at room temperature, during which time the
solution had turned yellow and a fine white precipitate had formed.
The latter was removed by centrifugation and the solution was
worked up as in (a) to give 11 (60 mg, 40%). The white precipitate,
which is insoluble in all common organic solvents, was washed
with CH2Cl2 and dried in vacuo to give 66 mg of product (14). The
tentative formulation of 14 as a polymeric isomer of cis-2 is based
on the 31P-MAS spectrum: d 19.1 (s, JPtP 2119 Hz), −61.0 (s, JPtP
1118 Hz).
[Pt2(l-2-C6H4PPh2)2(CNtBu)2] 18. A solution of 16 (718.1 mg,
0.50 mmol) in toluene (10 mL) was treated in portions with ButNC
(100.8 mg, 137.1 lL, 1.2 mmol) at room temperature. After ca.
10 min the originally cloudy solution became clear and after ca.
20 min a pale yellow precipitate of 18 started to appear. The
mixture was stirred for 3 h at room temperature, the solvent was
removed in vacuo, and the residue was washed with THF–hexane
(2 : 3) (3 × 20 mL); it was then dried in vacuo. The yield of 18 was
442 mg (82%). 1H NMR (CD2Cl2) d 1.1 (s, 18H, Me), 6.5–7.9 (m,
28H, aromatics); (C6D6) d 0.74 (Me); 13C NMR (CD2Cl2) d 29.7
(CMe3), 56.2 (CMe3), 148 (CNBut), 128–142 (aromatics); (C6D6)
d 29.2 (CMe3), 55.2 (CMe3); IR (KBr, cm−1) 2125 vs (C≡N str),
1560 w, 725 s.
[Pt2(l-I)(l-C6H3-5-Me-2-PPh2)2(PPh3)2]I [20]I. A solution of
17 (200 mg, 0.137 mmol) in CH2Cl2 (30 mL) was treated with
a solution of iodine (35 mg, 0.138 mmol) in CH2Cl2 (15 mL).
The mixture was stirred for 10 min and the solvent was removed
in vacuo. The residue was recrystallised from CH2Cl2–hexanes to
give [20]I as an orange solid (195 mg, 83%). 1H NMR (CDCl3) d
1.53 (s, 6H, Me), 6.2–7.8 (m, 56H, aromatics); MALDI-MS (m/z)
1592 [M − I]+.
[Pt2(l-H)(l-2-C6H4PPh2)2L2]Y (L = ButNC [21]+, PPh3 [22]+;
Y = various anions). (a) A suspension of 18 (215.4 mg,
0.15 mmol) in ether (15 mL) was treated with HBF4·OEt2
(24.3 mg, 0.15 mmol), causing the colour to change from yellow
to almost colourless. The slurry was stirred overnight. The solid
was separated by filtration, washed with ether (3 × 20 mL), and
dried in vacuo. The yield of [21]BF4 was 140 mg (80%).
[Pt(CO)(jC-C6H3-6-Me-2-PPh2)(j2-C6H3-6-Me-2-PPh2)2] 15.
When carbon monoxide was bubbled through a suspension of
cis-3 (50 mg, 0.067 mmol) in CH2Cl2 (4 mL) for 5 min, the
solid immediately dissolved to give an almost colourless solution.
Removal of solvent in vacuo gave 15 as a white solid (51 mg, 100%);
continued pumping led to loss of CO and formation of trans-3. 31
P
NMR (CD2Cl2) d −12.3 (d, JPP 2.3 Hz, JPtP 179 Hz, uncoord. P),
−62.4 (d, JPP 2.2 Hz, JPtP 1130 Hz, coord. P); IR (KBr, cm−1) 3046
m, 2952 m, 2921 m (C–H str), 2053 s (C≡O str), 1566 w (arom
+
=
C C str), 723 s (C–H def); EI-MS (m/z) 773 [M] , 745 [M −
(b) A suspension of 16 (161.8 mg, 0.15 mmol) in ether (15 mL)
was treated with HBF4·OEt2, CF3SO3H or p-MeC6H4SO3H
CO]+.
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Table 6 Crystal and structure refinement data for cis-[Pt(j2-C6H3-n-Me-2-PPh2)2] (n = 5, 2; n = 6, 3), [Pt2(j2-2-C6H4PPh2)2(l-2-C6H4PPh2)2] 10,
[Pt2(l-C6H3-5-Me-2-PPh2)2(PPh3)2] 17 and [Pt2(l-H)(l-C6H3-5-Me-2-PPh2)2(PPh3)2]PF6 [23]PF6
2
3
10
17
[23]PF6
Chemical formula
C38H32P2Pt
C38H32P2Pt
C72H56P4Pt2
C74H62P4Pt2
C74H63P4Pt2·PF6·H2O·
0.48C4H10O
1664.97
Orthorhombic
Pbca
M
745.71
Triclinic
¯
P1
745.71
Triclinic
C2/c
21.0147(5)
9.7799(3)
15.0753(4)
90
92.0661(12)
90
3096.29(15)
4
1435.31
Orthorhombic
Ibca
20.1950(3)
23.2688(3)
24.9714(3)
90
1465.38
Monoclinic
P21/n
12.6553(1)
23.2268(2)
20.6302(2)
90
93.1174(3)
90
6055.11(9)
4
Crystal system
Space group
˚
a/A
8.9749(1)
9.0823(1)
21.0062(3)
96.5555(8)
96.9372(7)
109.3427(8)
1581.92(4)
2
16.4610(1)
34.3557(2)
25.2509(1)
90
90
90
14 280.12(13)
8
200
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
U/A
Z
T/K
90
90
3
˚
11 734.4(2)
8
200
200
200
200
Yellow plate
Colour, habit
Colourless diamond shaped plate Colourless block
Yellow needle
Colourless needle
Crystal dimensions (mm) 0.30 × 0.20 × 0.10
0.18 × 0.13 × 0.05 0.30 × 0.12 × 0.10 0.14 × 0.10 × 0.07 0.42 × 0.11 × 0.04
D
calc/g cm−3
1.565
1.600
1.625
1.607
1.549
4.09
l/mm−1
4.543
4.661
4.897
4.765
Total reflections
Unique reflections
Used reflections
No. parameters
R (used reflections)
Goodness of fit
wR (used reflections)
44 162
28 035
113 538
124 161
138 093
9261 (Rint = 0.08)
7951 [I > 2r(I)]
370
0.0306
0.961
0.0361
1.19, −1.95
3575 (Rint = 0.08)
2996 [I > 3r(I)]
187
0.0246
1.0817
0.0281
1.65, −1.09
6720 (Rint = 0.065) 13 877 (Rint = 0.05) 16 360 (Rint = 0.06)
5589 [I > 3r(I)]
352
8705 [I > 3r(I)]
721
0.0174
1.088
0.0174
7479 [I > 3r(I)]
843
0.0227
1.079
0.0235
0.0398
1.935
0.0534
1.89, −1.08
−3
˚
qmax, qmin/e A
0.43, −0.48
0.69, −0.40
(0.15 mmol) and the mixture was worked up as under (a). The
Hydrogen atoms attached to carbon atoms were included at
idealised positions and ride on those carbon atoms. Where
appropriate peaks were observed in difference maps, the methyl
groups were oriented to best-fit these peaks, and the other methyl
groups were given the same orientations. A peak attributable to the
hydride was observed in the structure of [23]PF6. This atom was
included and allowed to refine positionally with the restraint that
the two Pt–H distances should be equal. This restraint accounts
for the small e.s.d.’s accociated with the hydride.
The disorder of the phenyl and p-tolyl groups in [23]PF6
was evident from the occupancies of less than unity for methyl
groups attached to both C(114) and C(134), as well as to C(214)
and C(234). The relative occupancies were refined in each case,
anisotropic displacement factors being used for the major sites
and isotropic for the minor. The ligands containing phosphorus
atoms P(3) and P(4) appear to be exclusively triphenylphosphine.
−
−
colourless solids [22]Y (Y = BF4−, CF3SO3 or p-MeC6H4SO3
)
were isolated in 80–90% yield.
[Pt2(l-H)(l-C6H3-5-Me-2-PPh2)2(PPh3)2]PF6 [23]PF6 (mixture
of isomers). To a stirred suspension of 17 (200 mg, 0.137 mmol)
in ether (30 mL) was added HPF6 (60% aq, 1 drop) in ether (5 mL).
The yellow colour faded almost immediately. After the mixture
had been stirred for 24 h, the colourless solid was separated by
filtration, washed with ether and dried in vacuo. The yield of
1
[23]PF6 was 215 mg (98%). H NMR (CD2Cl2) d −5.22 (m, JPH
6.3, 80.7 Hz, JPtH 735 Hz, 1H, PtH), 1.57 (s, Me), 2.26 (s, Me),
2.54 (s, Me) (total 6H), 7.0–8.0 (m, 56H, aromatics); 31P NMR
(CD2Cl2) d 3.0 (PA) (JAX ca. 1700 Hz), 23.5 (PB) (JBX ca. 3900 Hz,
JBX ca. 400 Hz); MALDI-MS (m/z) 1465 [M − PF6]+. X-Ray
ꢀ
quality crystals were grown from CH2Cl2–ether.
X-Ray crystallography
Acknowledgements
Data were collected at 200 K on a Nonius-Kappa CCD diffrac-
tometer using graphite-monochromated Mo Ka radiation (k =
Dr David Berry is acknowledged for spectral simulations carried
out at the University of Victoria, British Columbia, Canada, the
in-house program for which was made available by Dr Keith
Dixon. The solid state 31P NMR spectra were obtained by Dr
James Hook at the University of New South Wales.
0.71073 A) and were measured by means of COLLECT.56 Selected
˚
crystal data and details of data collection and structural refinement
are in Table 6.‡ The intensities of the reflections were extracted
and the data were reduced by use of the programs Denzo and
Scalepack.57 The structures of 2 and 10 were solved by heavy
atom Patterson methods (PATTY), expanded by standard Fourier
synthesis (DIRDIF 92)58 and refined on F with use of TEXSAN;59
the structures of 3, 17 and [23]PF6 were solved by direct methods
(SIR 92)60 and refined on F by use of the program CRYSTALS.61
References
1 F. Mohr, S. H. Prive´r, S. K. Bhargava and M. A. Bennett, Coord. Chem.
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‡ CCDC reference numbers 645529–645533. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b702808c
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