Organoplatinum chemistry with a dicarboxamide-diphosphine ligand: Hydrogen bonding, cyclometalation, and a complex with two metal-metal donor-acceptor bonds

Article abstract of DOI:10.1021/om400780q

The chemistry of the ligand bis(2-diphenylphosphinoethyl)phthalamide, dpppa, with platinum(II) is described. The reaction of dpppa with [Pt ₂Me₄(μ-SMe₂)₂], 1, in a 2:1 ratio gave a mixture of [PtMe₂(dpppa)] and [Pt₂Me ₄(μ-dpppa)₂], both of which contain Pt···H-N hydrogen bonds. However, reaction in a 1:1 ratio gave a remarkable tetraplatinum complex, [Pt₄Me₆(μ- dpppa-H)₂], which is shown to contain two Pt-Pt donor-acceptor bonds and in which one arm of the dpppa ligand has been cyclometalated. The reaction of [PtCl₂(dpppa)] with silver trifluoroacetate, to abstract chloride, and triethylamine as base has given the bis(cyclometalated) complex [Pt(dpppa-2H)], and this has been crystallized in three different forms, in which one or both of the carbonyl groups act as donors to a proton or to silver(I). The complex [Pt(dpppa-2H)]·AgO₂CCF ₃·dmso forms a dimer and [Pt(dpppa-2H)]·(AgO ₂CCF₃)₂ forms a coordination polymer in the solid state.

Full text of DOI:10.1021/om400780q

Article
pubs.acs.org/Organometallics
Organoplatinum Chemistry with a Dicarboxamide−Diphosphine
Ligand: Hydrogen Bonding, Cyclometalation, and a Complex with
Two Metal−Metal Donor−Acceptor Bonds
Nasser Nasser, Paul D. Boyle, and Richard J. Puddephatt*
Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7
S
* Supporting Information
ABSTRACT: The chemistry of the ligand bis(2-diphenylphosphinoethyl)-
phthalamide, dpppa, with platinum(II) is described. The reaction of dpppa with
[Pt2Me4(μ-SMe2)2], 1, in a 2:1 ratio gave a mixture of [PtMe2(dpppa)] and
[Pt2Me4(μ-dpppa)2], both of which contain Pt···H−N hydrogen bonds. However,
reaction in a 1:1 ratio gave a remarkable tetraplatinum complex, [Pt4Me6(μ-dpppa-
H)2], which is shown to contain two Pt−Pt donor−acceptor bonds and in which one
arm of the dpppa ligand has been cyclometalated. The reaction of [PtCl2(dpppa)]
with silver trifluoroacetate, to abstract chloride, and triethylamine as base has given
the bis(cyclometalated) complex [Pt(dpppa-2H)], and this has been crystallized in three different forms, in which one or both of
the carbonyl groups act as donors to a proton or to silver(I). The complex [Pt(dpppa-2H)]·AgO2CCF3·dmso forms a dimer and
[Pt(dpppa-2H)]·(AgO2CCF3)2 forms a coordination polymer in the solid state.
Chart 1. Examples of Phosphine−Carboxamide Ligands
INTRODUCTION
■
Ligands that contain both a phosphine and an amine or
carboxamide group are proving to be useful in catalysis or
molecular materials for sensing and other applications.1 The
phosphine groups are typically used to bind to transition metal
ions, while the carboxamide groups engage in hydrogen
bonding, with the role of recognizing substrates for catalysis
or sensing or to increase dimensionality in molecular
materials.1,2 Some typical examples are shown in Chart 1.
The simplest ligands contain one phosphine and one
carboxamide, as in dpb and bdp.3 However, more complex
examples, such as dpfca (Chart 1), which contains two
phosphines and one carboxamide group, have also been
used.1,3 Diphosphine dicarboxamide ligands, such as dppbH,4
have been studied, and chiral analogues, such as the Trost and
Morimoto ligands (Chart 1), have proved to be particularly
useful in catalysis.5 The application of the related para-, meta-,
and ortho-substituted dicarboxamide ligands dppeta, dpipa, and
dpppa (Chart 1) in the synthesis of coordination and
supramolecular polymers has also been reported.6 All of these
diphosphine dicarboxamide ligands can act as cis or trans
chelating ligands or as bridging diphosphine ligands, while the
carbonyl group can also coordinate, and the NH groups can act
as hydrogen bond donors or can be deprotonated to give amido
complexes.1−6
The versatility of the ligands dpipa and dppeta (Chart 1) in
organometallic chemistry has been established earlier.6 For
example, some chemistry of dpipa with the dimethylplatinum-
(II) complex [Pt2Me4(μ-SMe2)2], 1, is illustrated in Scheme 1.
The reaction with stoichiometry dpipa:1 = 2:1 gave an
equilibrium mixture of monomeric and dimeric
dimethylplatinum(II) complexes A and B, each of which
contained an unusual NH··Pt hydrogen bond. Heating this
mixture caused loss of methane with formation of the PNC-
pincer complex C, in which each ligand is doubly cyclo-
metalated by activation of an N−H bond and an aromatic C−H
Received: August 2, 2013
Published: September 13, 2013
© 2013 American Chemical Society
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Scheme 1. Some Organometallic Chemistry of the Ligand
dpipa
Scheme 2. Synthesis of Complex 3
a
6.89, consistent with a hydrogen-bonded structure.2−4,6,8 The
ESI-MS of complex 3 dissolved in dichloromethane gave a
major peak at m/z = 818.1, which corresponds to the ion
[PtCl(dpppa)]+, formed by loss of chloride from complex 3.
The structure of complex 3 is shown in Figure 1. It confirms
the cis chelate structure in which each phosphine is trans to
a
Stoichiometry dpipa:1 is 2:1 to form A, B, C and 1:1 to form D, E.
Figure 1. View of the structure of complex 3, with 30% probability
ellipsoids. Selected bond parameters (Å and deg): Pt(1)−Cl(1)
2.3623(9), Pt(1)−Cl(2) 2.362(1), Pt(1)−P(2) 2.258(1), Pt(1)−P(1)
2.2534(9); Cl(1)−Pt(1)−Cl(2) 86.35(3), Cl(1)−Pt(1)−P(2)
88.20(3), P(2)−Pt(1)−P(1) 97.82(3), P(1)−Pt(1)−Cl(2) 87.59(3).
Hydrogen bond distances: Cl(1)···N(2) 3.157(3), Cl(2)···N(1)
3.358(3) Å. The estimated hydrogen bond angles are N(1)H(1)Cl(2)
148° and N(2)H(2)Cl(1) 128°.
bond. On the other hand, the reaction with stoichiometry
dpipa:1 = 1:1 in dmso solution gave an intermediate, tentatively
identified as D, which eliminated methane on heating to give
the bis-PNC-pincer complex E, in which each dpipa ligand has
been quadruply cyclometalated by activation of both N−H
bonds and two aromatic C−H bonds.6
This paper reports a study of related organoplatinum
chemistry of the ligand dpppa (Chart 1). Its dimethylplatinum-
(II) complexes feature similar NH···Pt hydrogen bonding to
that in complexes A and B (Scheme 1), but the cyclometalation
chemistry involves only the N−H bonds, and an unexpected
complex containing two platinum−platinum donor−acceptor
bonds was formed.
chloride. The P−Pt−P angle of P(2)−Pt(1)−P(1) 97.82(3)° is
not greatly distorted from the ideal 90°, considering the large
13-membered ring resulting from chelation. The conformation
of the ligand is such that the NH groups are directed toward
the chloride ligands, with distances Cl(1)···N(2) 3.157(3) Å
and Cl(2)···N(1) 3.358(3) Å. These distances are clearly
different, but both are in the accepted range of 3.1−3.4 Å for
NH···Cl hydrogen bonds.9
The reaction of dpppa with [Pt2Me4(μ-SMe2)2] in a 2:1 ratio
gave a mixture of products, from which the monomeric and
dimeric dimethylplatinum(II) complexes 4a and 4b were
crystallized and structurally characterized (Scheme 3, Figures
2 and 3). Both complexes have cis-PtMe2P2 coordination, but
the monomer 4a has chelating dpppa (Figure 2) and the dimer
4b has bridging dpppa ligands (Figure 3). The two halves of the
RESULTS AND DISCUSSION
■
The reaction of dpppa with cis/trans-[PtCl2(SMe2)2], 2a, in 1:1
ratio gave the complex [PtCl2(dpppa)], 3, according to Scheme
2. In the 31P NMR spectrum, complex 3 gave a singlet
1
resonance at δ(31P) = 1.69, with J(PtP) = 3630 Hz in the
range expected for a complex with phosphorus trans to
chloride.4,7 In the H NMR spectrum, the NH resonance was
1
at δ = 7.94, significantly shifted from the value for free dpppa of
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Scheme 3. Reaction of dpppa with [Pt2Me4(μ-SMe2)2] in 2:1
Ratio
Figure 3. View of the structure of complex 4b, with 30% probability
ellipsoids. Selected bond parameters (Å and deg): Pt(1)−P(1)
2.310(1), Pt(1)−P(2) 2.297(1), Pt(1)−C(2) 2.083(6), C(1)−Pt(1)
2.109(4), Pt(1)···N(1) 3.258(4), Pt(1)···N(2) 5.329(3); P(2)−
Pt(1)−C(2) 90.1(1), P(2)−Pt(1)−P(1) 99.56(4), P(1)−Pt(1)−
C(1) 89.0(1), C(1)−Pt(1)−C(2) 81.2(2). Symmetry equivalent: 1−
x, −y, −z.
Figure 2. View of the structure of complex 4a, with 30% probability
ellipsoids. Selected bond parameters (Å and deg): Pt(1)−C(1)
2.106(4), Pt(1)−C(2) 2.110(3), Pt(1)−P(2) 2.300(1), Pt(1)−P(1)
2.306(1), Pt(1)···N(1) 3.599(3), Pt(1)···N(2) 3.463(3); P(1)−
Pt(1)−P(2) 98.31(3), C(1)−Pt(1)−C(2) 82.4(1), P(1)−Pt(1)−
C(1) 90.6(1), P(2)−Pt(1)−C(2) 88.75(9)°.
dimer 4b are related by a center of inversion. Both complexes
4a and 4b have one NH···Pt hydrogen bond for each
dimethylplatinum(II) unit, and the ligand must twist to allow
the short NH···Pt contact (compare Figures 2 and 3). In
complex 4a (Figure 2) the two Pt···N distances are similar
[Pt(1)···N(1) 3.599(3), Pt(1)···N(2) 3.463(3) Å], but the
estimated Pt···H distances are not [Pt(1)···H(1) 3.57, Pt(1)···
H(2) 2.65 Å] since only H(2) is oriented toward the platinum
center. In complex 4b (Figure 3), the NH···Pt bond appears
somewhat stronger, with Pt(1)···N(1) 3.258(4) Å and
estimated Pt(1)···H(1) 2.47 Å. In complex 4a, the only
hydrogen bond is the NH···Pt bond, but, in complex 4b, there
are also two intramolecular NH···OC hydrogen bonds, with
O(1)···N(2) and O(1A)...N(2A) 2.772(4) Å, and also a weaker
hydrogen bond to a chloroform solvate molecule with O(1)···
C(1S) 3.12 Å. The NH···Pt hydrogen bonding in the dpppa
complexes 4a and 4b is directly comparable to that in the
related dpipa complexes A and B (Scheme 1).
Figure 4. 31P NMR spectra (162 MHz, CDCl3 solution, 298 K) of (a)
the initial mixture obtained in the reaction of Scheme 3; (b) the
crystals of 4a; (c) the crystal mixture of 4a and 4b.
both 4a and 4b (Figure 4c). Thus 4a gives a sharp singlet
resonance at δ(31P) = 7.08, 1J(PtP) = 1814 Hz, while 4b gives a
1
broad singlet resonance at δ(31P) = 10.28, J(PtP) = 1760 Hz.
The isomers interconvert only slowly at room temperature. The
low values of 1J(PtP) are characteristic of platinum(II)
complexes with the phosphine trans to a methyl group.7 In
the initial 31P NMR spectrum (Figure 4a), the resonances for
4a and 4b are observed, but two additional singlet resonances
are also present, labeled F [δ(31P) = 11.18, 1J(PtP) = 1790 Hz]
The 31P NMR spectrum for the initial mixture of products of
reaction of dpppa with [Pt2Me4(μ-SMe2)2] in 2:1 ratio is
shown in Figure 4a and was initially difficult to interpret.
However, recrystallization gave two batches of crystals, one
containing only 4a (Figure 4b) and one containing crystals of
1
and G [δ(31P) = 11.80, J(PtP) = 1800 Hz], for which the
coupling constants also indicate phosphine trans to methyl, but
these peaks could not be assigned and the compounds could
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not be obtained in pure form. The ESI-MS of the initial
reaction mixture dissolved in dichloromethane gave two major
peaks at m/z = 798.2, which corresponds to the ion
[PtMe(dpppa)]+, and at m/z = 1649.4, which corresponds to
the ion [Pt2Me4(dpppa)2]Na+. These peaks are consistent with
the presence of a mixture of 4a and 4b, but they give no insight
into the structures of F and G.
In order to observe a single 31P NMR resonance, each
complex 4a and 4b must undergo dynamic exchange of the
hydrogen bond between the N(1)H and N(2)H donors. At
−80 °C, the monomer (4a) still showed a single resonance in
the 31P NMR spectrum, but the dimer (4b) gave two broad
resonances [δ(31P) = 14.6, 1J(PtP) ≈ 1920 Hz and 3.9, 1J(PtP)
≈ 1670 Hz], with a coalescence temperature of about −60 °C,
giving, from the Eyring equation, an approximate activation
energy of 9 kcal mol−1. The fluxionality for 4b involves breaking
both NH···Pt and both NH··OC hydrogen bonds and then
twisting the ligands to form the symmetry-equivalent hydrogen
bonds, whereas for 4a it only involves twisting of the ligand to
replace one NH···Pt hydrogen bond by another. It is not
surprising therefore that fluxionality is more difficult for 4b.
The reaction of dpppa with [Pt2Me4(μ-SMe2)2], 1, in 1:1
ratio again gave a mixture of products, including 4a and 4b, but
the 31P NMR spectrum indicated the formation of a new
complex, 5, which gave two resonances at δ(31P) = 23.63,
Figure 5. Structure of complex 5, with 30% probability ellipsoids. The
phenyl groups are not shown, for clarity. Selected bond parameters (Å
and deg): Pt(1)−Pt(2) 2.6491(7), Pt(1)−P(1) 2.164(3), Pt(1)−N(1)
2.098(8), Pt(1)−C(1) 2.06(1), Pt(2)−P(3) 2.327(3), Pt(2)−O(1)
2.149(7), Pt(2)−C(2) 2.03(1), Pt(2)−C(3) 2.07(1), Pt(3)−Pt(4)
2.6495(9), Pt(3)−P(4) 2.159(3), Pt(3)−N(4) 2.105(9), Pt(3)−C(4)
2.05(1), Pt(4)−P(2) 2.325(3), Pt(4)−O(4) 2.150(7), Pt(4)−C(5)
2.03(1), Pt(4)−C(6) 2.08(1), N(1)−C(9) 1.30(1), O(1)−C(9)
1.31(1), N(2)−C(16) 1.34(1), O(2)−C(16) 1.24(1), N(3)−C(45)
1.34(1), O(3)−C(45) 1.24(1), N(4)−C(52) 1.28(4), O(4)−C(52)
1.30(1), N(2)···O(4) 2.77, N(3)···O(1) 2.76; P(1)−Pt(1)−Pt(2)
168.08(8), P(4)−Pt(3)−Pt(4) 168.00(8).
1J(PtP) = 3230 Hz, J(PtP) = 1380 Hz, J(PP) = 8 Hz, and
δ(31P) = 2.87, 1J(PtP) = 926 Hz, 3J(PP) = 8 Hz.
Recrystallization gave a mixture of colorless crystals of 4a and
yellow crystals of 5. The ESI-MS of the isolated crystals of
complex 5 dissolved in dichloromethane, with NaI added, gave
a major peak at m/z = 2067.4, which corresponds to the ion
[Pt4Me6(dpppa-H)2]Na+. Complex 5 was finally characterized
to be [{Me2Pt(μ3-κ4-P,O,N,P-Ph2PCH2CH2NHCOC6H4CON-
CH2CH2PPh2)PtMe}2] by a structure determination. The
formation of 5 is depicted in Scheme 4. It involves activation
2
3
acceptor metal−metal bond, with the dimethylplatinum center
as donor and the monomethylplatinum center as acceptor.11
Each platinum(II) center then has the favored 16-electron
configuration. Some related examples (H, I, J) are shown in
Chart 2, but the formation of the donor−acceptor bond during
cyclometalation and the presence of two donor−acceptor
bonds in the same molecule appear to be unprecedented.11
Scheme 4. Synthesis of Complex 5
Chart 2. Compounds H, I, and J with Donor−Acceptor
Bonds, and a Diplatinum(III) Complex K (ON = amidate)
of one N−H bond of each dpppa ligand and one
methylplatinum bond of 1, with elimination of methane, and
displacement of the dimethylsulfide ligands from 1.
The remarkable structure of complex 5, which crystallized as
a chloroform solvate, is shown in Figure 5. There are four
platinum atoms in the molecule, two having square pyramidal
PtMe2POPt coordination and two having square planar
PtMePNPt coordination. Each Pt−Pt bonded unit can be
considered as a “T-over-square” complex containing a donor−
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While the coordination of the amide nitrogen in 5 was not
unexpected,4,6 the coordination of the carbonyl group to the
soft platinum center was a surprise. Each Pt−Pt donor−
acceptor bond is supported by the bridging amidate N−CO
unit. Bridging amidates are well known in inorganic complexes,
including diplatinum(III) complexes (complex K, Chart 2) and
related platinum blues, but they are uncommon in organo-
platinum chemistry.12 In the bridging amidate groups, the NC
bonds [N(1)−C(9) 1.30(1), N(4)−C(52) 1.28(1) Å] are on
average slightly shorter than the CO bonds [O(1)−C(9)
1.31(1), O(4)−C(52) 1.30(1) Å], whereas in the amide groups
the CO bonds are shorter [N(2)−C(16) 1.34(1), O(2)−C(16)
1.25(1), N(3)−C(45) 1.28(1), O(3)−C(45) 1.24(1) Å],
indicating that both resonance forms shown in Scheme 4 are
significant. The Pt−Pt distances [Pt(1)−Pt(2) 2.6491(7),
Pt(3)−Pt(4) 2.6495(9) Å] are comparable to those in related
complexes [2.769(1) Å in H; 2.6491(4) Å in I, Chart 2].11 The
distance Pt(1)−P(1) 2.164(3) Å is short, and comparison with
distances in 3, 4a, and 4b indicates that the trans-influence
Scheme 5. Synthesis of Complex 6 and Its Silver(I) Adducts
series is Me− (4a, 4b) > Cl− (3), NR2 (7, 8, 9, see below) >
−
PtMe2PO (5), and thus that the platinum donor has a
particularly low trans-influence. This is consistent with the large
1
value of the coupling constant J(PtP) = 3230 Hz for the P(1)
atom in 5.7 The two remaining NH groups in 5 are hydrogen
bonded to carbonyl groups [N(2)···O(4) 2.77, N(3)···O(1)
2.76 Å], and the other two carbonyl groups are weakly
hydrogen bonded to chloroform solvate molecules [O(2)···
C(1X) 3.17, O(3)···C(1Y) 3.13 Å]. The NH···OC hydrogen
bonds are intramolecular but interligand, in contrast to 4b, in
which intraligand hydrogen bonding is observed (Figure 3).
The formation of complex 5 (Scheme 4) involves elimination
of methane, by combination of N−H and Pt−Me groups. In
principle, elimination of methane from 4a, 4b, or 5 could give
further amidoplatinum(II) complexes. However, heating
complex 4a/4b to 140 °C in dmso gave only partial reaction,
and no pure products could be obtained. Greater success was
achieved by reaction of [PtCl2(dpppa)], 3, with silver
trifluoroacetate and triethylamine, as shown in Scheme 5.
The reaction gives derivatives of the complex [Pt{κ4-PNNP-
C6H4-1,2-(CONCH2CH2PPh2)2}], 6. However, although 6 has
been isolated in pure form after addition of LiCl to remove
silver ions, it has not been possible to crystallize 6 in its simple
form. The complex binds to silver, and the adducts 7 = 6·
AgO2CCF3·dmso·0.5C6H6, when dmso was present in the
recrystallization solvent mixture, or 8 = 6·(AgO2CCF3)2, when
no dmso was present, were formed instead (Scheme 5). When
the reaction was carried out as in Scheme 5, but with lithium
chloride added to precipitate the remaining silver compounds
corresponds to 62+AgO2CCF3+H+, and complex 7 gave a peak
at m/z = 2003.1, which corresponds to 62+(AgO2CCF3)2+H+.
In the adduct 9, Figure 6, there is a molecule of 6 (Figure 6a)
and a molecule of [6·Et3NOH]+ (Figure 6b), in which the
Pt(1) molecule of 6 is strongly hydrogen bonded to the
Et3NOH+ cation [O(1A)···O(1XA) 2.603(8) Å]. The structure
confirms that the complex has the diamido-diphosphine-
platinum(II) coordination observed previously in related
compounds.4 The structure contains two five-membered rings
and one seven-membered ring in the boat conformation, and
this structure is also observed in the silver(I) adducts 7 and 8.
The structure of complex 7 is shown in Figure 7. It can be
considered to contain a Ag2(μ-dmso)2 core,13 with each silver
ion coordinated by a trifluoroacetate ion on one side and by a
carbonyl group from a molecule of complex 6 on the other.
In the structure of complex 8, there are two crystallo-
graphically independent molecules of 6, each of which is
coordinated first to an Ag2(O2CCF3)2 unit using both carbonyl
groups as ligands (Figure 8). In the Pt(1) molecule, which is
also depicted in Scheme 5, one trifluoroacetate ligand bridges
between silver(I) ions, with Ag(1)−O(5A) 2.247(4) and
Ag(2)−O(6A) 2.227(3) Å, while the other bridges and also
chelates to Ag(2), with Ag(1)−O(3A) 2.405(4), Ag(2)−
O(3A) 2.572(5), and Ag(2)−O(4A) 2.536(4) Å. In the
Pt(2) molecule, one trifluoroacetate bridges between silver(I)
ions, with Ag(3)−O(5B) 2.434(5) and Ag(4)−O(6B) 2.392(5)
Å, while the other bridges through a single oxygen donor, with
Ag(3)−O(3B) 2.333(5) and Ag(4)−O(3B) 2.308(4) Å.
The building blocks of [6·(AgO2CCF3)2], which are
illustrated in Figure 8, undergo self-association to give
coordination polymers, as shown for the Pt(1) molecules in
Figure 9. Each carbonyl oxygen donor bridges between
−
as AgCl, crystals of the adduct 9 = 62·Et3NOH+CF3CO2 ·H2O·
CHCl3 (Figure 6) could be obtained. It seems that the carbonyl
groups in complex 6 are basic and tend either to bind to Ag+ in
7 and 8 or to engage in hydrogen bonding in 9. The Et3NOH+
ion in 9 is identified crystallographically and is presumed to be
formed by oxidation of triethylamine during recrystallization in
−
the presence of Et3NH+CF3CO2 . Single crystals of the pure
complex 6 could not be obtained, but it and its derivatives 7, 8,
and 9 have very similar NMR spectra. For example, the 31P
NMR spectra for 9 and 8 in CDCl3 solution gave δ(31P) =
1
1
31.27, J(PtP) = 3100 Hz, and δ(31P) = 30.80, J(PtP) = 3110
Hz, respectively, while complex 7 in dmso-d6 gave δ(31P) =
31.04, 1J(PtP) = 3090 Hz. In the ESI-MS, complexes 7, 8, and 9
all gave a major peak at m/z = 782.2, which corresponds to
6+H+, complexes 7 and 8 gave a peak at m/z = 1783.2, which
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Figure 7. View of the structure of complex 7, with 30% probability
ellipsoids. Phenyl groups attached to phosphorus atoms are omitted
for clarity. Selected bond parameters (Å and deg): Pt(1)−P(1)
2.2483(9), Pt(1)−P(2) 2.2340(9), Pt(1)−N(1) 2.044(2), Pt(1)−
N(2) 2.059(2), Ag(1)−O(3) 2.314(3), Ag(1)−O(2) 2.212(2),
Ag(1)−O(5) 2.573(5), Ag(1)−O(5A) 2.342(4) Å; P(1)−Pt(1)−
P(2) 102.45(2), P(1)−Pt(1)−N(1) 83.88(6), N(1)−Pt(1)−N(2)
92.99(8), N(2)−Pt(1)−P(2) 79.91(6), O(2)−Ag(1)−O(3)
120.1(1), O(5)−Ag(1)−O(3) 104.5(1), O(5)−Ag(1)−O(3)
94.7(1), O(5)−Ag(1)−O(2) 96.7(1), Ag(1)−O(5)−Ag(1) 98.0(1),
O(5)−Ag(1)−O(5) 82.0(1)°.
cyclooctadiene)] with dppbH (Chart 1), without the need for
added base, and it is not easily protonated.4 Complex 6
contains two five-membered and one seven-membered chelate
ring, while L contains one five-membered and two six-
membered rings. Both 6 and L contain essentially planar
nitrogen atoms, and more extensive delocalization of the pπ
lone pair is possible in L, which has extra phenylene groups
compared to 6.4 Structural data suggest that hydrogen bonding
or coordination of 6 to E+ (Chart 3, E = H or Ag) gives
resonance forms M and N, with significant contribution from
the imine form N. Thus in the Pt(1) molecule of 9 (E =
Et3NOH+, Figure 6), the distance N(1A)−C(3A) = 1.312(6) Å
is shorter than N(2A)−C(10A) = 1.347(6) Å and O(1A)−
C(3A) = 1.262(6) Å is longer than O(2A)−C(10A) = 1.242(5)
Å, and in complex 7 (E = Ag+, Figure 7), N(2)−C(10) =
1.321(3) Å is shorter than N(1)−C(3) = 1.337(3) Å and
O(2)−C(10) = 1.267(3) Å is longer than O(1)−C(3) =
1.245(3) Å.
Figure 6. Views of the two platinum compounds in 9: (a) the Pt(2)
molecule of 6 and (b) the Pt(1) molecule of [6·Et3NOH]+, with 30%
probability ellipsoids. Selected bond parameters (Å and deg): Pt(1)−
P(1A) 2.235(1), Pt(1)−P(2A) 2.236(1), Pt(1)−N(2A) 2.071(3),
Pt(1)−N(1A) 2.049(3), N(1X)−O(1X) 1.414(7); N(1A)−Pt(1)−
N(2A) 92.6(1), N(1A)−Pt(1)−P(1A) 79.72(9), P(2A)−Pt(1)−
N(2A) 83.91(9), P(2A)−Pt(1)−P(1A) 103.14(4). For the Pt(2)
molecule, which has no strong H-bonds: Pt(2)−P(1B) 2.242(1),
Pt(2)−P(2B) 2.241(1), Pt(2)−N(1B) 2.048(3), Pt(2)−N(2B)
2.051(3); N(1B)−Pt(2)−N(2B) 93.3(1), N(1B)−Pt(2)−P(1B)
79.91(9), P(1B)−Pt(2)−P(2B) 102.84(4), N(2B)−Pt(2)−P(2B)
83.2(1).
A feature of the chemistry of the dimethylplatinum
complexes is that the electron-rich platinum(II) center tends
to act as a nucleophile in forming hydrogen bonds in complexes
4a and 4b or in forming donor−acceptor metal−metal bonds in
complex 5. Some DFT calculations were carried out, using the
Becke−Perdew (BP) functional, with scalar relativistic
correction, to gain some insight into these unusual bonds.
The Pt···HN hydrogen bonds in 4a and 4b were modeled by
using cis-[PtMe2(PMe3)2] as the platinum center and N-
methylformamide as the amide. The calculation predicts that, in
the model adduct (Figure 10c), Pt···H = 2.39 Å and Pt···N =
3.43 Å, which are similar to the distances Pt···H = 2.65, 2.47 Å
and Pt···N = 3.46, 3.26 Å in 4a and 4b, respectively. The
bonding energy is calculated to be 8 kcal mol−1 in the model
complex, in the usual range for a hydrogen bond.8 The key
equivalent silver(I) ions to give four-membered Ag2(μ-6)2
rings, with Ag(1)−O(1A) 2.410(4) and Ag(1A)−O(1A)
2.429(4) Å on one side and Ag(2)−O(2A) 2.310(3) and
Ag(2B)−O(2A) 2.472(4) Å on the other side. There is a center
of symmetry at the middle of each four-membered ring.
Repetition of this self-assembly gives rise to the polymer, and
the Pt(2) molecules undergo the same type of self-assembly to
give a very similar polymer. Overall, in the Pt(1) polymer, the
Ag(1) centers are four-coordinate [Ag(1)O(1A)O(1AA)O-
(3A)O(5A)] and the Ag(2) centers are five-coordinate
[Ag(2)O(2A)O(2AB)O(3A)O(4A)O(6A)], while in the
Pt(2) polymer, both silver ions are four-coordinate [Ag(3)O-
(1B)O(1BA)O(3B)O(5B) and Ag(4)O(2B)O(2BB)O(3B)O-
(6B)].
2
The analogous diamido−diphosphine complex of platinum-
(II), L, Chart 3, appears to be much less basic than 6. Thus
complex L forms spontaneously by reaction of [PtCl2(1,5-
frontier orbitals are the filled 5dz orbital of platinum (Figure
10e) as nucleophile and the σ*(NH) orbital of the amide
(Figure 10d) as electrophile. The calculated HOMO of the
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Chart 3. Diamido−Diphosphine Complexes and Adducts
with E+ (E = Et3NOH+ or Ag+)
Figure 8. Views of the structure of complex 8, with 30% probability
ellipsoids. Above, the Pt(1) molecule and, below, the Pt(2) molecule.
Selected bond distances (Å): Pt(1)−P(1A) 2.244(2), Pt(1)−P(2A)
2.249(1), Pt(1)−N(1A) 2.071(4), Pt(1)−N(2A) 2.055(5), Ag(1)−
O(3A) 2.405(4), Ag(1)−O(5A) 2.247(4), Ag(1)−O(1A) 2.410(4),
Ag(1)−O(1AA) 2.429(4), Ag(2)−O(4A) 2.536(4), Ag(2)−O(3A)
2.572(5), Ag(2)−O(2A) 2.310(3), Ag(2)−O(2AB) 2.472(4), Ag(2)−
O(6A) 2.227(3); Pt(2)−P(1B) 2.249(2), Pt(2)−P(2B) 2.250(1),
Pt(2)−N(1B) 2.058(3), Pt(2)−N(2B) 2.057(5), Ag(3)−O(3B)
2.333(5), Ag(3)−O(5B) 2.434(5), Ag(3)−O(1B) 2.432(4), Ag(3)−
O(1BA) 2.381(4), Ag(4)−O(6B) 2.392(5), Ag(4)−O(3B) 2.308(4),
Ag(4)−O(2B) 2.450(3), Ag(4)−O(2BB) 2.302(5).
Figure 10. Calculated structures and some frontier orbitals for (a, d)
structure and σ*(NH) orbital of HCONHMe; (b, e) structure and
HOMO of cis-[PtMe2(PMe3)2]; (c, f) structure and HOMO of the H-
bonded complex.
adduct (Figure 10f) and electron transfer of 0.05e from
platinum donor to amide acceptor are consistent with the
formulation of the Pt···HN interaction as a hydrogen bond, but
not as an agostic interaction, and this is supported by the
calculated linear Pt···H−N geometry (Figure 10c).10
The formation of one of the PtPt donor−acceptor bonds in
complex 5 has been modeled in terms of the combination of
fragments PtMe(Me2 PCH2CH2 NCOMe), O, and
PtMe2(PMe3), P, to give the amidate-bridged PtPt bond in
model complex Q, in which each fragment acts as both donor
Figure 9. Part of the polymeric structure of complex 8, showing the
Pt(1) molecules only. The Pt(2) molecules form a very similar
polymer.
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and acceptor in forming the Pt−Pt and Pt−O bonds (Scheme
6).
Scheme 6. Model for Formation of One of the PtPt Donor−
Acceptor Bonds in Complex 5
Some of the frontier orbitals involved are shown in Figure 11,
while an orbital correlation energy diagram is shown in Figure
12. The HOMO in both O and Q has the character of N and O
pπ and platinum dπ orbitals and is primarily nonbonding in both
2
(Figures 11a,b 12). The HOMO in P is the platinum 5dz
orbital (Figure 11d), which interacts with the LUMO of the 14-
electron fragment O, which is a 5d6s6p hybrid orbital (Figure
11c), to form the PtPt donor−acceptor bond, with associated
bonding and antibonding MOs (Figure 11e,f). The comple-
mentary Pt−O bond is formed by donation from the HOMO−
1 orbital of O (Figure 11g) to the LUMO of P, which is a
5d6s6p hybrid orbital (Figure 11h), with the resulting bonding
MO illustrated in Figure 11i. There are also interactions
between filled dπ orbitals of the two fragments, but these are
mostly nonbonding overall (Figure 12). The overall bonding
energy, which is the sum of the Pt−Pt and Pt−O bonding
energies, is calculated to be 64 kcal mol−1. The yellow color of
complex 5 arises from the transition from the HOMO (Figure
11b) to the low-lying Pt−Pt σ* molecular orbital (Figures 11f
and 12).
CONCLUSIONS
■
The chemistry described illustrates the nucleophilic character of
the platinum(II) center in dimethylplatinum(II) complexes by
formation of hydrogen bonds in the complexes
[PtMe2(dpppa)], 4a, and [Pt2Me4(μ-dpppa)2], 4b, and Pt−Pt
donor−acceptor bonds in [Pt4Me6(μ-dpppa-H)2], 5. The
isolation of complex 5 also illustrates how the cyclometalation
of dpppa occurs in a stepwise manner, though the doubly
cyclometalated complex [Pt(dpppa-2H)] can be isolated only
from the chloride precursor [PtCl2(dpppa)]. [Pt(dpppa-2H)]
is also electron rich and forms interesting complexes with
silver(I) through coordination of one or both of the carbonyl
groups.
Figure 11. Frontier orbitals for model reagents and product in Scheme
6: (a, b) the HOMO in O, Q; (c, d) the acceptor orbital in O and
donor orbital in P in forming the PtPt bond; (e, f) the resulting
bonding and antibonding orbitals in Q; (g, h) the donor orbital in O
and acceptor orbital in P in forming the PtO bond; (i) the resulting
bonding orbital in Q.
EXPERIMENTAL SECTION
■
Reagents and General Procedures. All reactions were carried
out in an inert atmosphere of dry nitrogen using standard Schlenk
techniques, unless otherwise specified. All solvents used for air- and
moisture-sensitive materials were purified using an Innovative
Technology Inc. PURE SOLV solvent purification system. NMR
spectra were recorded at ambient temperature, unless otherwise noted
(ca. 25 °C), by using Varian Mercury 400 or Varian Inova 400 or 600
corrections.15 The energy minima were confirmed by vibrational
frequency analysis in each case.
X-ray Crystallography (ref 16). The sample was mounted on a
Mitegen polyimide micromount with a small amount of Paratone N
oil. X-ray data were collected at 110 K with ω and φ scans using a
Bruker Smart Apex II diffractometer and Bruker SMART software or a
Nonius Kappa-CCD diffractometer with COLLECT software, using
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Unit cell
parameters were calculated and refined from the full data set.
Reflections were scaled and corrected for absorption effects using
SADABS. All structures were solved by either Patterson or direct
methods with SHELXS or the SIR2011 program and refined by full-
matrix least-squares techniques against F2 using SHELXL. All non-
hydrogen atoms were refined anistropically. The hydrogen atoms,
including the NH hydrogen atoms, were not located but were placed
1
spectrometers. H chemical shifts are reported relative to TMS, and
31P chemical shifts relative to 85% H3PO4. Mass spectrometric analysis
was carried out using an electrospray PE-Sciex mass spectrometer
(ESI-MS) coupled with a TOF detector. Analyses were performed at
́
́
Laboratoire d’Analyse Elementaire, Montreal. The ligand dpppa and
complexes [PtCl2(SMe2)2] and [Pt2Me4(μ-SMe2)2] were prepared as
described previously.6,14 DFT calculations were carried out by using
the Amsterdam Density Functional program based on the BLYP
functional, with double-ζ basis set and first-order scalar relativistic
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g, 83%. NMR in dmso-d6: δ(1H) = 7.94 [br, 2H, NH]; 7.72−7.82 [m,
4H, C6H4]; 7.17−7.58 [m, 20H, Ph]; 3.72 [m, 4H, NCH2]; 2.99 [m,
1
4H, CH2P]; δ(31P) = 1.69 [s, JPtP = 3630 Hz]. Single crystals of
complex 3 were grown by slow diffusion of n-pentane into a solution
of the compound dissolved in a mixture of solvents: benzene,
dimethylsulfoxide, methanol, acetone, dichloromethane, and chloro-
form (0.1 mL of each). Anal. Calcd for C36H34Cl2N2O2P2Pt: C, 50.60;
H, 4.01; N, 3.28. Found: C, 50.87; H, 3.76; N, 3.02.
[PtMe2(dpppa)], 4a, and [Pt2Me4(μ-dpppa)2], 4b. To a solution of
dpppa (0.10 g, 0.17 mmol) in CH2Cl2 (10 mL) was added a solution
of [Pt2Me4(μ-SMe2)2] (0.0488 g, 0.085 mmol) in CH2Cl2 (10 mL).
The solution was allowed to stir for 12 h., and the solvent was
removed under vacuum to give a white solid product, which was
washed with ether (3 × 5 mL) and pentane (3 × 5 mL) and then dried
under high vacuum. Yield (4a+4b): 0.12 g, 87%. NMR in CDCl3: 4a,
δ(1H) = 7.61 [br s, 2H, NH]; 7.42 −7.60 [m, 4H, C6H4]; 7.30−7.09
[m, 20H, Ph]; 3.92 [m, 4H, NCH2]; 2.70 [m, 4H, CH2P]; 0.21 [m,
6H, 2JPtH = 66 Hz, 3JPH = 6 Hz, PtCH3]; δ (31P) = 7.08 [s, 1JPtP = 1814
Hz]. 4b, δ(1H) = 8.11 [br s, 4H, NH]; 7.70−7.79 [m, 4H, C6H4];
7.36−7.03 [m, 44H, Ph and C6H4]; 3.68 [br m, 8H, NCH2]; 2.52 [br
2
3
m, 8H, CH2P]; 0.46 [m, 12H, JPtH = 67 Hz, JPH = 7 Hz, PtCH3];
δ(31P) = 10.28 [s, 1JPtP = 1760 Hz]. Anal. Calcd for C76H80N4O4P4Pt2:
C, 56.09; H, 4.95; N, 3.44. Found: C, 56.22; H, 4.75; N, 3.15. Single
crystals of both complexes 4a and 4b were grown by slow diffusion of
n-pentane into a solution of the compound dissolved in chloroform;
typically, single crystals of both 4a and 4b were present in a given
batch of crystals with the ratio dependent on concentration used.
[Pt4Me6(μ-dpppa-H)2], 5. To a solution of dpppa (0.10 g, 0.17
mmol) in CH2Cl2 (10 mL) was added a solution of [Pt2Me4(μ-
SMe2)2] (0.10 g, 0.17 mmol) in CH2Cl2 (10 mL). A mixture of yellow
and white precipitates was obtained after allowing the solution to stir
for ca. 10 h. The yellow precipitate was isolated by crystallization.
Yield: 0.078 g, 45%. Single crystals of complex 5 were grown by slow
diffusion of n-pentane into a solution of the impure compound
dissolved in chloroform. NMR in CDCl3: δ(1H) = 8.37 [br s, 2H,
NH]; 7.70−7.21 [m, 48H, Ph and C6H4]; 4.17 [m, 4H, NCH2]; 3.10
[m, 4H, NCH2]; 2.70 [m, 4H, PCH2]; 2.27 [m, 4H, PCH2]; 0.79 [d,
Figure 12. Energy correlation diagram for formation of model
complex Q.
6H, 2JPtH = 50 Hz, 3JPH = 9 Hz, PtMe trans to P]; 0.63 [s, 6H, 2JPtH
=
in calculated positions and refined using the riding model; the
hydrogen atoms are not usually shown in the figures. Crystal data are
summarized in the cif files. Unusual features are as follows. The
asymmetric unit of complex 5 contains four CHCl3 molecules, one of
which is disordered. The disorder was successfully modeled. For
complex 5, CheckCIF gives an A level alert due to high-amplitude
motion in one of the phenyl rings. The difference map did not give any
peaks in this region that could be used to model a possible disorder, so
there was no way to address this alert. Complex 7 exhibits both
positional and compositional disorders. The Ag atom was disordered
over three sites, denoted as Ag1, Ag1′, and Ag1″. The occupancies
were refined until they were stable in the least-squares. To prevent
high correlation with ADPs, they were normalized to 1.0 and fixed for
subsequent refinement cycles. The occupancies were 0.83533, 0.08734,
and 0.07733 for Ag1, Ag1′, and Ag1″, respectively. In addition, the
ADP parameters for the silver atoms were constrained to be equal. In
addition to the positional disorder, the complex exhibits compositional
disorder wherein a dmso and a SMe2 molecule occupy the same region
of the asymmetric unit. The methyl groups of the dmso and the SMe2
were coincident. The SMe2 is bonded to Ag1′, and therefore the
occupancy of that moiety was set equal to the occupancy of the Ag1′
site. Similarly, the dmso-bridged Ag1 sites, which were related by a
crystallographic inversion center, and the occupancy of the dmso
molecule were set equal to the occupancy of the Ag1 site. Because the
silver is disordered over three sites and the sulfurs are disordered over
two sites, the occupancies for the DMSO and the SMe2 do not sum to
1.0. This is why the formula contains fractional numbers for C, H, and
S.
82 Hz, PtMe trans to N]; 0.08 [s, 6H, 2JPtH = 54 Hz, PtMe trans to O];
δ (31P) = 23.63 [d, 1JPtP = 3230 Hz, 2JPtP = 1380 Hz, 3JPP = 8 Hz]; 2.87
[d, 1JPtP = 926 Hz, 3JPP = 8 Hz]. Anal. Calcd for C78H84N4O4P4Pt4: C,
45.79; H, 4.14; N, 2.74. Found: C, 45.69; H, 4.31; N, 2.52.
[Pt{κ4-N,N,P,P-C6H4-1,2-(CONCH2CH2PPh2)}]2, 6, and 9 = 62·
Et3NOH+CF3CO2−·H2O·CHCl3. To a solution of 3 (0.10g, 0.11
mmol) dissolved in CH2Cl2 (2 mL), acetone (2 mL), and methanol
(2 mL) was added a solution of silver trifluoroacetate (0.052 g, 0.23
mmol) in THF (5 mL). After allowing the reaction to stir for 1 h,
triethylamine (33 μL, 0.23 mmol) in CH2Cl2 (2 mL) was added to the
reaction contents. Two hours after the triethylamine addition, lithium
chloride (0.02 g, 0.47 mmol) in methanol (5 mL) was added. The
reaction was allowed to stir overnight (ca. 16 h). AgCl precipitate was
removed by filtration, the filtrate was collected, solvents were
evaporated, and the product 6 was isolated as a colorless solid,
washed with pentane (3 × 5 mL) and ether (3 × 5 mL), and dried
under high vacuum. Yield: 0.08 g, 87%. NMR in CDCl3: δ(1H) = 7.53
[m, 2H, C6H4]; 7.05−7.25 [m, 22H, Ph and C6H4]; 3.02 [m, 4H,
1
NCH2]; 2.31 [m, 4H, CH2P]; δ(31P) = 31.27 [s, JPPt = 3100 Hz].
Anal. Calcd for C36H32N2O2P2Pt: C, 55.32; H, 4.13; N, 3.58. Found:
C, 55.08; H, 4.10; N, 3.32. Single crystals of complex 9 were grown by
slow diffusion of n-pentane into a solution of a similar reaction mixture
dissolved in chloroform.
[ P t { κ 4 - N , N , P , P - C 6 H 4 - 1 , 2 - ( C O N C H 2 C H 2 P P h 2 ) } ] 2 ·
Ag2(OCOCF3)2(OSMe2)2, 7. To a solution of 3 (0.10g, 0.12 mmol)
dissolved in CH2Cl2 (2 mL), acetone (2 mL), methanol (2 mL), and
dmso (0.2 mL) was added a solution of silver trifluoroacetate (0.16 g,
0.70 mmol) in THF (5 mL). After allowing the reaction to stir for 1 h,
triethylamine (0.10 mL, 0.70 mmol) in CH2Cl2 (2 mL) was added to
the reaction contents. The reaction was allowed to stir overnight (ca.
10 h.). The formed AgCl precipitate was removed by filtration. The
filtrate was collected, solvents were evaporated, and the product was
[PtCl2(dpppa)], 3. To a stirred solution of dpppa (0.10 g, 0.17
mmol) in acetone (10 mL) was added a solution of cis/trans-
[PtCl2(SMe2)2] (0.061 g, 0.17 mmol) in acetone (10 mL). The
precipitate of complex 3 was collected, washed with pentane (3 × 5
mL) and ether (3 × 5 mL), and dried under high vacuum. Yield: 0.12
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isolated as a colorless solid. The product was washed with pentane (3
× 5 mL) and ether (3 × 5 mL) and dried under high vacuum. Yield:
0.11 g, 86%. NMR in dmso-d6: δ(1H) = 6.94−7.59 [m, 48H, Ph and
C6H4]; 3.11 [m, 8H, NCH2]; 2.50 [m, 12H, (CH3)2SO]; 2.17 [m, 8H,
CH2P]; δ(31P) = 31.04 [s, 1JPPt = 3090 Hz]. Single crystals of complex
7 were grown by slow diffusion of n-pentane into a solution of the
compound dissolved in dichloromethane, chloroform, and benzene
(0.1 mL of each). Anal. Calcd for C80H76Ag2F6N4O10P4Pt2S2: C,
44.46; H, 3.54; N, 2.59. Found: C, 44.64; H, 3.80; N, 2.50.
Chem. 2013, 52, 7051. (c) Nasser, N.; Boyle, P. D.; Puddephatt, R. J.
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[Pt{κ4-N,N,P,P-C6H4-1,2-(CONCH2CH2PPh2)2}Ag2(OCOCF3)2]n, 8.
To a solution of 3 (0.10 g, 0.12 mmol) dissolved in CH2Cl2 (2
mL), acetone (2 mL), and methanol (2 mL) was added a solution of
silver trifluoroacetate (0.16 g, 0.70 mmol) in THF (5 mL). After
allowing the reaction to stir for 1 h, triethylamine (0.1 mL, 0.70 mmol)
in CH2Cl2 (2 mL) was added to the reaction contents. The reaction
was allowed to stir overnight (ca. 10 h). The formed AgCl precipitate
was removed by filtration. The filtrate was collected, solvents were
evaporated, and the product was isolated as a colorless solid. The
product was washed with pentane (3 × 5 mL) and ether (3 × 5 mL)
and dried under high vacuum. Yield: 0.12 g, 83%. NMR in CDCl3:
δ(1H) = 8.02 [t, 3JHH = 6 Hz, 2H, C6H4]; 6.85−7.77 [m, 22H, Ph and
C6H4]; 4.86 [m, 4H, NCH2]; 2.60 [m, 4H, CH2P]; δ(31P) = 30.80 [s,
1JPPt = 3110 Hz]. Single crystals of complex 5 were grown by slow
diffusion of n-pentane into a solution of the compound dissolved in
dichloromethane and chloroform (0.1 mL of each). Anal. Calcd for
C80H64Ag4F12N4O12P4Pt2: C, 39.27; H, 2.64; N, 2.29. Found: C, 39.02;
H, 2.78; N, 2.54.
ASSOCIATED CONTENT
* Supporting Information
CIF files in electronic form only are available free of charge via
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S
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail (R.J.P.): pudd@uwo.ca.
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the NSERC (Canada) for financial support.
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