η2-Allenyl- and η2-Alkynylphosphonium Complexes of Platinum

Aug 21, 2013 - Research School of Chemistry, The Australian National University, Canberra, Australian Capital Territory 0200, Australia. ‡ X-ray Dif...
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η2‑Allenyl- and η2‑Alkynylphosphonium Complexes of Platinum Annie L. Colebatch,† Ian A. Cade,† Anthony F. Hill,*,† and Mohan M. Bhadbhade‡ †

Research School of Chemistry, The Australian National University, Canberra, Australian Capital Territory 0200, Australia X-ray Diffraction Laboratory, Mark Wainwright Analytical Centre, The University of New South Wales, Kensington, New South Wales 2052, Australia

‡

S Supporting Information *

ABSTRACT: The reaction of the propargylic salt [Ph3PCH2CCH]PF6 with [Pt(C2H4)(PPh3)2] affords the η 2 -allenylphosphonium salt [Pt(η 2-CH 2CCHPPh 3)(PPh3)2]PF6 via a metal-mediated propargylic rearrangement. Isomerization of the complex occurs in solution to generate the salt [Pt{η2-C(PPh3)CCH2}(PPh3)2]PF6, wherein the allene is coordinated by the internal CC bond. Computational studies indicate that the isomerization of the propargylic cation [Ph3PCH2CCH]+ to the allenyl species [Ph3PCHC CH2]+ and the α-alkynyl isomer [Ph3PCCCH3]+ is thermodynamically favorable. The isomeric η2-alkynylphosphonium salt [Pt{η2-C(CH3)CPPh3}(PPh3)2]PF6 is formed from the reaction of [Ph3PCCCH3]PF6 with [Pt(C2H4)(PPh3)2] and does not isomerize to the propargylic or allenyl forms.

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Chart 2. Known Examples of η2-Allenylphosphonium Complexes (M = Cr, n = 3; M = Mo, n = 3, 5, 6)

INTRODUCTION Propargylic rearrangements are well documented throughout chemistry, and those involving propargylphosphonium salts have been the subject of a number of studies.1,2 Schweizer has reported that propargyltriphenylphosphonium bromide, [Ph3PCH2CCH]Br ([1]Br), can be isomerized to form the allenylphosphonium [Ph3PCHCCH2]Br ([2]Br) and the α-alkynylphosphonium [Ph3PCCCH3]Br ([3]Br) salts (Chart 1) via treatment with KOtBu or by heating in the Chart 1. Isomeric Structures: (a) Propargyl-, (b) Allenyl-, and (c) α-Alkynylphosphonium Salts

The literature hosts a scattering of reports of η 2 allenylphosphonium complexes (Chart 2),4 but these generally involve modification of a precoordinated ligand to form the C3P moiety. Krivykh and co-workers have published the syntheses of chromium and molybdenum allenylphosphonium salts via the photolytic displacement of a CO ligand from [M(C6H6−nMen)(CO)3] (M = Cr, n = 3; M = Mo, n = 3, 5, 6) in the presence of ROCH2CCH (R = H, Me) and PPh3.4a,b Manganese complexes of the type [Mn{η2-CH(PR3)C CPhR′}Cp(CO)2]BF4 (R = alkyl, aryl; R′ = H, Ph) have been similarly produced by this method4b and by protonation of η1allenylphosphonium salts.4c Esteruelas and Oro were able to protonate the acetylide ligand of [RhH(acac)(η 1 -C CCPh2OH)(PR3)2] (R = Cy, iPr), which underwent subsequent phosphine migration to give [Rh(acac){η2-CH(PR3) CCPh2}(PR3)]BF4.4d Finally, Wenger has shown that electrophilic addition of MeI to the alkynylphosphine complex [Pt(MeCCPPh 2)(dcpe)] results in formation of the

presence of phenol, respectively.1 Schweizer has also shown that the allenylphosphonium salt [2]Br is an intermediate in nucleophilic addition reactions to [1]Br. Indizhikyan and colleagues have reported that [Ph3PCH2CCR]Br (R = H, Ph) can undergo solvent-dependent propargylic rearrangements to form the isomeric allenyl or α-alkynyl salts.2 We have an ongoing interest in complexes containing unsaturated phosphonium ligands.3 We have previously reported the reaction of [1]Br with [Ru(CO)2(PPh3)3], in which coordination of [1]+ induced a propargylic rearrangement to the allenyl isomer to provide [Ru(η2-CH2C CHPPh3)(CO)2(PPh3)2]Br (Chart 2).3a Although isomerizations of [1]+ to [2]+ are known, this represents an isolated example of a metal-mediated isomerization and as such prompted a more detailed study into the coordination chemistry of [1]+. © 2013 American Chemical Society

Received: May 8, 2013 Published: August 21, 2013 4766

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platinum salt [Pt{η2-CH(PMePh2)CCH2}(dcpe)]I, in which the alkyne moiety has rearranged to the allene.4e In the present work we have studied the reactions of [1]+− [3]+ with platinum complexes. We find that platinum(0) also effects a propargylic rearrangement of [1]+ upon coordination to provide allenylphosphonium complexes.

half-life for conversion of [1]+ to [2]+ in CDCl3 is ca. 72 h, while the rearrangement does not appear to proceed in CD3CN. In scrupulously anhydrous THF, the half-life is ca. 60 min, while in “benchtop” grade THF, the conversion is complete within this time and traces of [3]+ are observed. This perhaps points to the operation of acid/base catalysis by adventitious water. Significant spontaneous isomerizations of [1]+ or [2]+ to [3]+ were never observed, and the synthesis of the α-alkynyl salt [1]Br was achieved using Schweizer’s protocol1 followed by anion exchange to afford [3]PF6. The three isomers are readily identifiable in both the 1H and 31 1 P{ H} NMR spectra. Resonances are observed at δP 22.3 for [1]PF6, δP 18.9 for [2]PF6, and δP 6.1 for [3]PF6. Characterization of [2]PF6 included an X-ray crystallographic study (Figure 2), the bond lengths and angles of which are unremarkable.

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RESULTS AND DISCUSSION For our investigations into the coordination chemistry of propargylphosphonium salts, [1]Br was synthesized for use as a starting material. However, we encountered problems with undesired coordination of the bromide counterion to metal complexes, as has been observed previously.5 To circumvent this, substitution of the bromide for a noncoordinating counterion was performed. Metathesis of Br− for PF6− was achieved by treatment of an aqueous solution of [1]Br with an excess of NaPF6 to provide [1]PF6 as a white precipitate (Scheme 1). Aside from aromatic resonances, the 1H NMR Scheme 1. Syntheses of Phosphonium Salts

Figure 2. Molecular structure of [2]+ in a crystal of [2]PF6 (50% displacement ellipsoids, phenyl groups and PF6− counterion omitted for clarity). Selected bond lengths (Å) and angles (deg): P1−C3 = 1.781(2), C2−C3 = 1.297(3), C1−C2 = 1.286(4), P1−C1−C2 = 122.58(18), C1−C2−C3 = 178.7(3), P1−C3−C1−H31c = 94(2), P1−C3−C1−H32c = 85(2).

spectrum of [1]PF6 shows a doublet of doublets at 4.25 ppm for the PCH2 group and a doublet of triplets at 2.30 ppm assigned to the terminal CCH group. Characterization of [1]PF6 included a single-crystal X-ray study (Figure 1) that,

In our work with [1]PF6 we found it to be thermally sensitive to nucleophilic attack, as noted by Schweizer1 and Indzhikyan.2 Small quantities of the products of methanolysis [Ph3PCH2C(CH2)OCH3]PF6 ([4]PF6; Figure 3) and hydrolysis

Figure 1. Molecular structure of [1]+ in a crystal of [1]PF6 (50% displacement ellipsoids, phenyl groups and PF6− counterion omitted for clarity). Selected bond lengths (Å) and angles (deg): P1−C3 = 1.826(8), C2−C3 = 1.440(13), C1−C2 = 1.169(14); P1−C3−C2 = 114.2(7), C1−C2−C3 = 177.2(12). Figure 3. Molecular structure of [4]+ in a crystal of [4]PF6 (50% displacement ellipsoids, phenyl groups and PF6− counterion omitted for clarity). Selected bond lengths (Å) and angles (deg): P1−C3 = 1.814(3), C3−C2 = 1.481(4), C1−C2 = 1.317(5); P1−C3−C2 = 111.7(2), C1−C2−C3 = 125.8(3).

while of low precision, nevertheless confirmed the identity. The structure of the bromide analogue [1]Br has been reported,6 and there are no significant differences in the geometric parameters of the P−C3 unit between the two structures. For comparison, the allenyl and α-alkynyl isomers [2]PF6 and [3]PF 6 were synthesized (Scheme 1). Schweizer synthesized [2]Br by treating [1]Br with a catalytic amount of KOtBu.1 We found that [1]PF6 isomerized to [2]PF6 upon standing in solution without the deliberate addition of base. However, this isomerization does appear to be solventdependent, as also observed by Indizhikyan and colleagues in their studies of propargylphosphonium salts.2 Specifically, the

[Ph3PCH2C(CH2)OC(CH3)CHPPh3](PF6)2 ([5](PF6)2; Figure 4) were isolated and characterized during purification attempts in which [1]PF6 was heated to 50 °C (Scheme 2). Both [4]PF 6 and [5](PF 6 ) 2 are consistent with the intermediacy of [2]+ in nucleophilic additions to [1]+ demonstrated by Schweizer. 4767

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To investigate the reactivity of propargylphosphonium salts toward group 10 metals, we initially explored the reaction of [1]+ with [Pt(C2H4)(dcpe)], as this would be expected to provide the closest comparison to the previously reported salt [Pt{η2-CH(PMePh2)CCH2}(dcpe)]I.4e Unfortunately, NMR spectra of the reaction mixture indicated that a large number of products were formed and we were unable to isolate a single product. Reaction of [1]PF6 with the slightly less hindered complex [Pt(C2H4)(PPh3)2] resulted in formation of [Pt(η2-CH2CCHPPh3)(PPh3)2]PF6 ([6]PF6) in 92% yield (Scheme 3) via a metal-mediated propargylic rearrangement.

Figure 4. Molecular structure of [5]2+ in a crystal of [5](PF6)2 (50% displacement ellipsoids, phenyl groups and PF6− counterions omitted for clarity). Selected bond lengths (Å): P1−C21 = 1.824(3), C21− C22 = 1.492(4), C22−C23 = 1.303(4), P2−C48 = 1.759(3), C48− C49 = 1.333(4), C49−C50 = 1.494(4).

Scheme 3. Syntheses of Platinum Allenylphosphonium Salts

Scheme 2. Solvolysis of Propargylphosphonium Salts

To gain a better understanding of these isomerizations, the relative energies of the three isomers [1]+−[3]+ were calcuated.7 The optimized structures reproduce the geometries obtained in the crystal structures of [1]X (X = Br,6 PF6) and [2]PF6. The calculated relative energies (Figure 5) show that

Interestingly, the allenylphosphonium ligand is coordinated through the terminal CC group, whereas in Wenger’s complex [Pt{η2-CH(PMePh2)CCH2}(dcpe)]I coordination via the internal CC moiety is observed. The 31P{1H} NMR spectrum exhibits four distinct resonances due to the three PPh3 groups and the PF6− anion. The resonance due to the phosphonium group is observed as a doublet at 15.1 ppm, displaying a comparatively strong coupling (4JPP = 55.4 Hz) to the phosphorus nucleus of the pseudo-trans PPh3 ligand. In the 1 H NMR spectrum the CH2 and CH groups of the allene moiety are observed at 1.49 ppm (multiplet) and 5.37 ppm (dddt), respectively. The 195Pt NMR spectrum of [6]PF6 shows a doublet of doublets of doublets of doublets of triplets (ddddt) at −4684 ppm with the platinum coupling constants observed in the 1H and 31P{1H} NMR spectra reproduced in the 195Pt NMR spectrum. Saito and co-workers have reported the 195Pt chemical shifts for a serious of 16 acetylene complexes [Pt(RCCR′)(PPh3)2], ranging from −4741 ppm for R = R′ = Ph to −4479 ppm for R = R′ = CN.8 The chemical shift of [6]PF6 of −4684 ppm falls within this range, as is expected for an electron-withdrawing alkene. This is further verified by comparison with [Pt(CF2CF2)(PPh3)2] (δPt −4791),9 in which an electron-withdrawing alkene is coordinated. In the precursor [Pt(CH2CH2)(PPh3)2], in which the alkene is not particularly π-acidic, the platinum resonance is observed further upfield at −5065 ppm.10 These data suggest that the allenylphosphonium ligand behaves as a comparatively π-acidic alkene. The crystal structure determination of [6]PF6 (Figure 6) was of low precision, precluding detailed analysis of geometric features, but does reveal that the allene lies in the P1−Pt1−P2 coordination plane, as is found in the structure of the parent

Figure 5. Relative energies (ΔG, kJ/mol) of the isomeric cations [1]+−[3]+.7

the isomerizations [1]+ → [2]+ (−27.47 kJ/mol) and [2]+ → [3]+ (−4.25 kJ/mol) are exergonic in the gas phase. It is thus not surprising that these rearrangements occur and it is conceivable that the process could therefore be mediated by an appropriate catalyst. The driving force for these isomerizations is presumably the desire for conjugation of the unsaturated bonds with the phosphorus heteroatom. 4768

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Figure 6. Molecular structure of [6]+ in a crystal of [6]PF6· 0.15CH2Cl2 (50% displacement ellipsoids, phenyl groups, solvate, and PF6− counterion omitted for clarity). Selected bond lengths (Å) and angles (deg): Pt1−C1 = 2.10(2), Pt1−C2 = 1.94(3), C1−C2 = 1.47(3), C2−C3 = 1.34(3), C3−P3 = 1.74(3); C1−Pt1−C2 = 42.4(8), Pt1−C1−C2 = 63.0(13), Pt1−C2−C3 = 149.2(18), C1− C2−C3 = 136(2), C2−C3−P3 = 130.8(19).

Figure 7. Molecular structure of S-[8]+ in a crystal of rac-[8]PF6· 1.5CH2Cl2 (50% displacement ellipsoids, phenyl groups, solvate, and PF6− counterion omitted for clarity, R-enantiomer generated by crystallographic P1̅ symmetry). Selected bond lengths (Å) and angles (deg): Pt1−C2 = 2.012(3), Pt1−C3 2.127(3), C1−C2 = 1.309(4), C2−C3 = 1.455(4), C3−P1 = 1.759(3); C2−Pt1−C3 = 41.05(12), Pt1−C2−C3 = 73.73(16), C1−C2−Pt1 = 145.8(3), C1−C2−C3 = 140.3(3), C2−C3−P1 = 116.9(2).

allene complex [Pt(η2-CH2CCH2)(PPh3)2].10 This is consistent with the chemical nonequivalence of the two PPh3 ligands observed in the 31P{1H} NMR spectrum. A comparison of these two structures shows no significant difference in the bond lengths and angles of the P−C3-Pt unit. The synthesis of a κ2C,C′ isomer of [6]+, [Pt{κ2-CH C(PPh3)CH2}(PPh3)2]BF4 ([7]BF4), has been reported by Chen and co-workers via nucleophilic attack of PPh3 on the allenyl salt [Pt(η3-HCCCH2)(PPh3)2]BF4.11 A solution of [6]PF6 at 50 °C was monitored by NMR spectroscopy to observe whether formation of [7]PF6 could be induced by the thermal isomerization of [6]PF6. After 1 day, peaks appeared corresponding not to [7]PF6 but to the allenylphosphonium isomer [Pt{η2-C(PPh3)CCH2}(PPh3)2]PF6 ([8]PF6), wherein the allene is coordinated by the internal CC bond (cf. terminal coordination in [6]PF6) (Scheme 3). The 1H NMR spectrum of [8]PF6 comprises three distinct resonances at 5.86, 4.34, and 3.42 ppm, each of which appears as a multiplet with 195Pt satellites. In the 13C{1H} NMR spectrum the resonance due to the central allene carbon C appears at 158.4 ppm, a considerable upfield shift in comparison to the equivalent resonance in [6]PF6 at 197.9 ppm. A crystal structure determination of [8]PF6 (Figure 7) confirmed the coordination mode proposed on the basis of the spectroscopic data. As for [6]PF6, the allene C3 unit lies in the P2−Pt1−P3 coordination plane. The coordination of the phosphonium group one bond closer to the metal center in [8]PF6 in comparison to [6]PF6 would be anticipated to increase steric congestion. However, this is avoided because the bulky phosphonium group now lies below the coordination plane as a result of the orthogonal nature of allene terminal substituents. In fact, there is little deviation in the bond lengths and angles of the two alternative coordination modes, though the precision of the molecular structure for [6]PF6 was somewhat lower than for [8]PF6. In the structure of the free allene [2]PF6 the C1−C2−C3 spine is linear (sp hybridized C2), but this is considerably distorted upon coordination to the metal center, wherein C2 can be considered as sp2 hybridized. In [6]PF6 the C1−C2−C3 angle is 136(2)°, and in [8]PF6 this angle is 140.3(3)°, between the expected values for sp (180°) and sp2 (120°) hybridized carbon centers, the bending back of substituents being typical of coordination of a π system.

The conversion of [6]PF6 to [8]PF6 reached a plateau after 2 days and remained in the approximate ratio of 2:5 [6]PF6: [8]PF6, even after 1 month at 50 °C. At 100 °C formation of [8]PF6 was observed after 2 h, but unfortunately both compounds decompose at this temperature and complete conversion to [8]PF6 is not obtained. Notably, even under these forcing conditions no resonances due to [7]+ were observed in the course of the reaction. This implies that the isomerization of [6]+ to [8]+ does not involve intermolecular P−C bond cleavage, since liberated PPh3 would attack the central carbon of the C3 unit to form [7]+. The isomerization of [6]PF6 to [8]PF6 also occurred at ambient temperatures, but the conversion was much slower. The reaction of the allene [2]PF6 with [Pt(C2H4)(PPh3)2] also resulted in formation of the externally coordinated complex [6]PF6, rather than the equilibrium mixture of [6]PF6 and [8]PF6 that might have been expected. This indicates that [6]PF6 is the kinetic product and further supports the contention that the rearrangement of [6]+ to [8]+ does not proceed via dissociation of PPh3. Heating a solution of [8]PF6 to 50 °C resulted in the same isomeric distribution as was obtained upon heating [6]PF6. The mechanism for this isomerization is thought to be analogous to that proposed by Pettit for the [Fe(η2-CMe2 CCMe2)(CO)4] system, in which the Fe(CO)4 unit moves from one π bond to the orthogonal π bond.12 In contrast to what is observed here for [6]PF6 and [8]PF6, interconversion in Pettit’s system is very facile. In the 1H NMR spectrum at −60 °C signals for the coordinated and uncoordinated CMe2 groups are distinct but at 30 °C only one signal is seen, indicating that the Fe(CO)4 unit is moving rapidly between the two π bonds on the 1H NMR time scale. In Krivykh’s chromium and molybdenum systems conversion of the terminally to the internally coordinated isomers is slow and irreversible.4a,b Because a mixture of [6]+ and [8]+ is slowly achieved and then a constant composition is maintained at 50 °C, it may be concluded that this platinum system represents a slow but reversible conversion (K50 °C ≈ 2.5). Despite computational studies showing that [3]+ is the most stable of the three isomeric species in the gas phase, no 4769

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relative to that for the conventional ethylidyne carbon (2.027(4) Å). Despite the disparate steric profiles of the methyl and phosphonio substituents, the bend-back angles for the alkyne are similar (C1−C2−C3 = 144.0(4)°, C2−C3−P1 = 139.4(3)°). Heating a solution of [9]PF6 in CDCl3 at 50 °C fails to result in any spectroscopically detectable (1H NMR) isomerization to [6]PF6, [7]PF6, or [8]PF6 over a period of 14 days. Above this temperature (100 °C in DCl2CCCl2D), decomposition ensues, as was also observed for [6]PF6 under these conditions: i.e., were isomerization to occur, the product(s) would not be stable under these conditions. Kinetic barriers for interconversion of [6]+−[9]+ notwithstanding, why then are the allene isomers [6]+ and [8]+ apparently the most favored? In terms of the simple Dewar− Chatt−Duncanson model, the key bonding components comprise donation from the occupied π bonding orbital to platinum and retrodonation to the empty π* orbital. Experimentally, the extent to which these synergic interactions occur is manifested in a lengthening of the coordinated C−C multiple bond. Table 1 therefore presents the ratio of

evidence for formation of alkynylphosphonium species was observed throughout this work either as the free ligand [3]+ or coordinated to platinum. This is not due to the instability of [3]+ coordination, as we were able to independently isolate and structurally characterize (Figure 8) the η2-alkynylphosphonium salt [Pt{η2-C(CH3)CPPh3}(PPh3)2]PF6 ([9]PF6) in 91% yield from the reaction of [Pt(C2H4)(PPh3)2] with [3]PF6 (Scheme 4).

Table 1. Elongation of C−C Multiple Bonds upon Coordination to “Pt(PPh3)2” Figure 8. Molecular structure of [9]+ in a crystal of [9]PF6·CHCl3 (50% displacement ellipsoids, phenyl groups, solvate, and PF6− counterion omitted for clarity). Selected bond lengths (Å) and angles (deg): Pt1−C2 = 2.027(4), Pt1−C3 = 2.063(3), C1−C2 = 1.492(6), C2−C3 = 1.287(6), C3−P1 = 1.742(4); C2−Pt1−C3 = 36.66(16), Pt1−C2−C3 = 73.2(2), C1−C2−Pt1 = 142.6(3), C1−C2−C3 = 144.0(4), C2−C3−P1 = 139.4(3).

[1]+ term-[2]+ int-[2]+ [3]+

r1CC/Å, free (calcd)

r2CC/Å, X-ray

1.186 1.290 1.303 1.193

1.169 1.286 1.297

r3CC/Å, complex

r3/r1

1.470 1.455 1.287

1.14 1.12 1.08

experimentally determined coordinated C−C bond length vs that calculated for the free molecule, since we lack crystallographic data for [3]+. The complexes [6]+ and [8]+, in which the allenyl ligand is coordinated, show a 12−14% lengthening of the CC multiple bond upon coordination, in comparison to the free ligand [2]+. A smaller 8% lengthening of the CC bond is observed for the alkynylphosphonium complex [9]+ in comparison to the free alkynyl ligand [3]+. Figure 9 presents the relative energies of the relevant donor and acceptor orbitals. From this it may be seen that the energies of the donor orbitals are somewhat similar for all four potential ligands. The energies of the acceptor orbitals, however, span some 5 eV. The propargylphosphonium cation appears least accommodating with respect to retrodonation from platinum, perhaps explaining why a complex of [1]+ has yet to be isolated (See Experimental). Of the two distinct acceptor orbitals of [2]+, that associated with coordination of platinum to the internal CC bond is marginally lower in energy, consistent with both the terminal and internal coordination isomers coexisting in equilibrium. The alkynylphosphonium cation [3]+ would appear to be a weaker donor but a more effective π acceptor, accounting for the stability of [9]+. Interestingly, the allenylphosphonium salt [Pt{η2-CH(PMePh2)CCH2}(dcpe)]I is actually formed from the alkynylphosphine complex [Pt{η2-C(CH3)CPPh2}(dcpe)].4e When this alkynylphosphine complex is treated with MeI, alkylation occurs at the phosphine, but the resultant alkynylphosphonium complex is unstable and rearranges to the allene. This suggests that these types of propargyl− allenyl−α-alkynyl rearrangements are actually system-specific, as this isomerization observed by Wenger and colleagues is in the direction opposite (α-alkynyl to allenyl) to those seen in

Scheme 4. Synthesis of a Platinum Alkynylphosphonium Salt

The methyl group is evident in the 1H NMR spectrum as a doublet of doublets at 1.42 ppm. The PPh3 ligands appear in the 31P{1H} NMR spectrum as doublets of doublets at 24.4 and 24.0 ppm, while the phosphonium group lies upfield at 0.9 ppm. A strong trans-3JPP coupling of 61.5 Hz is observed which is much larger than the corresponding cis-3JPP coupling of 33.5 Hz and the geminal 2JPP coupling of 17.6 Hz. In the 13C{1H} spectrum a substantial difference of 80 ppm is seen between the two alkynyl carbon atoms. The carbon atom adjacent to the phosphonium group appears at 91.7 ppm, while the carbon atom adjacent to the methyl group is much further downfield at 172.0 ppm. In the propynylphosphine complex [Pt{η2C(CH3)CPPh2}(dcpe)] the two alkynyl carbon atoms appear at 117.6 and 145.6 ppm.4e The presence of the charged phosphonium moiety in [9]PF6 thus accentuates the disparity between the two alkynyl carbon nuclei. In the 195Pt NMR spectrum [9]PF6 appears at −4598 ppm, which is within the expected range for an electron-deficient alkyne.8 The crystal structure determination of [9]PF6 (Figure 8) reveals conventional η2-alkyne coordination (C2−C3 = 1.287(6) Å) in which the bond between platinum and the phosphonium-substituted carbon is elongated (2.063(3) Å) 4770

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constants given in Hz. While 13C{1H} signals for ortho and meta carbon nuclei of PPh3 groups could be routinely observed, their narrow spectral range and comparable JPC values often precluded unequivocal assignment, in which case they are designated as “C2,3,5,6(PPh3)”. Infrared spectra were obtained using a Perkin-Elmer Spectrum One FT-IR spectrometer. Elemental microanalytical data were obtained from the ANU Research School of Chemistry microanalytical service. Electrospray ionization mass spectrometry (ESI-MS) was performed by the ANU Research School of Chemistry mass spectrometry service with acetonitrile as the matrix. Data for Xray crystallography were collected with a Nonius Kappa CCD diffractometer or a Bruker Kappa-II CCD diffractometer. The compounds [Ph3PCH2CCH]Br,1 [Ph3PCCCH3]Br,1 and [Pt(C2H4)(PPh3)2]13 were prepared according to published procedures. All other reagents were obtained from commercial sources. All calculations were carried out using Gaussian 09.14 Geometry optimizations were performed using M06-2X/6-31+G(d,p).15 Energy calculations were carried out using the M0615 level of density functional theory with the 6-311++G(2d,2p) basis set for hydrogen and aug-cc-pVDZ basis set for carbon and phosphorus on the molecules in the gas phase at 298 K and 1 atm. Solution-phase calculations16 were performed in tetrahydrofuran and chloroform using M06/6-31+G(d,p).15 Frequency calculations were performed to confirm that the optimized structures represent genuine local minima. Synthesis of [Ph3PCH2CCH]PF6 ([1]PF6). A solution of NaPF6 (2.201 g, 13.10 mmol) in distilled water (50 mL) was added to a solution of [1]Br (2.500 g, 6.557 mmol) in distilled water (550 mL) with stirring. The product [1]PF6 formed immediately as a white precipitate, which was collected by vacuum filtration, washed thoroughly with distilled water, and dried under high vacuum. Crystals suitable for crystallographic analysis were obtained by diffusion of nhexane into a solution of [1]PF6 in CH2Cl2. Yield: 2.734 g (6.126 mmol, 93%). IR (Nujol; ν/cm−1): 3172 (CCH); 2219 (CC); 1440 (PCH2); 1114 (PPh); 838 (PF6). IR (CH2Cl2; ν/cm−1): 3174 (CCH); 2217 (CC); 1440 (PCH2); 1113 (PPh); 846 (PF6). 1H NMR (CDCl3; δ/ppm): 7.89−7.60 (m, 15H, C6H5); 4.25 (dd, 2H, PCH2, 2JPH = 15.3, 4JHH = 3.0); 2.30 (dt, 1H, CCH, 4JPH = 6.9, 4JHH = 3.0). 1H NMR (CD3CN; δ/ppm): 7.94−7.66 (m, 15H, C6H5); 4.34 (dd, 2H, PCH2, 2JPH = 16.0, 4JHH = 2.9); 2.67 (dt, 1H, CCH, 4JPH = 6.0, 4JHH = 2.9). 13C{1H} NMR (CD3CN; δ/ppm): 136.7 (d, C4(PPh3), 4JPC = 3.1); 134.8 (d, C2,3,5,6(PPh3), JPC = 10.3); 131.3 (d, C2,3,5,6(PPh3), JPC = 13.4); 118.0 (d, C1(PPh3), 1JPC = 83.5, partially obscured by CD3CN peak); 78.1 (d, CCH, 3JPC = 9.3); 72.2 (d, CCC, 2JPC = 13.5); 17.0 (d, PCH2, 1JPC = 57.7). 31P{1H} NMR (CDCl3; δ/ppm): 22.3 (s, PPh3); −143.7 (sep, PF6, 1JPF = 712.5). 31 1 P{ H} NMR (CD3CN; δ/ppm): 21.5 (s, PPh3); −144.6 (sep, PF6, 1 JPF = 707.9). MS-ESI(+): m/z 301.3 [M − PF6]+. Accurate mass: found 301.1146 [M − PF6]+, calcd for C21H18P 301.1146. Anal. Found: C, 56.62; H, 4.05; N, 0.00. Calcd for C21H18F6P2: C, 56.51; H, 4.06; N, 0.00. Crystal data for C21H18P·PF6: Mw = 446.31, monoclinic, P21/n, a = 15.5539(3) Å, b = 12.5279(3) Å, c = 22.6531(5) Å, β = 109.5520(11)°, V = 4159.60(16) Å3, Z = 8, ρcalcd = 1.43 Mg m−3, μ(Mo Kα) = 0.27 mm−1, T = 200(2) K, colorless plate, 0.40 × 0.27 × 0.04 mm, 7314 independent reflections, F2 refinement, R = 0.133, Rw = 0.2543 for 5646 reflections (I > 2σ(I), 2θmax = 50°), 542 parameters. Synthesis of [Ph3PCHCCH2]PF6 ([2]PF6). The title compound was obtained from the isomerization of [1]PF6 (18 mg, 40 μmol) in CH2Cl2 (1 mL) at room temperature. Crystals suitable for crystallographic analysis were obtained by diffusion of toluene into a solution of [2]PF6 in CH2Cl2. Yield: 17 mg (38 μmol, 94%). IR (Nujol; ν/cm−1): 1964 (CCC); 1440 (PCH2); 1114 (PPh); 838 (PF6). IR (CH2Cl2; ν/cm−1): 1960 (CCC); 1440 (PCH2); 1113 (PPh); 846 (PF6). 1H NMR (CDCl3; δ/ppm): 7.85−7.60 (m, 15H, C6H5); 6.45 (dt, 1H, PCH, 2JPH = 8.4, 4JHH = 6.6); 5.33 (dd, 2H, CH2, 4 JPH = 12.8, 4JHH = 6.6). 1H NMR (CD3CN; δ/ppm): 7.94−7.66 (m, 15H, C6H5); 6.55 (dt, 1H, PCH, 2JPH = 8.4, 4JHH = 6.8); 5.36 (dd, 2H, CH2, 4JPH = 12.8, 4JHH = 6.8). 13C{1H} NMR (CD3CN; δ/ppm): 219.2 (s, C); 136.4 (d, C4(PPh3), 4JPC = 2.0); 134.9 (d, C2,3,5,6(PPh3), JPC = 11.4); 131.2 (d, C2,3,5,6(PPh3), JPC = 10.3); 119.1 (d, C1(PPh3), 1JPC = 91.8); 81.0 (d, CH2, 3JPC = 14.5); 74.6 (d, PCH,

Figure 9. Topologies and relative energies (eV) of the donor and πacceptor orbitals presented for coordination to a metal center by [1]+, [2]+ (terminal and internal coordination) and [3]+.7

our system (propargyl to allenyl). This offers the attractive possibility of designing tunable systems to favor a specific isomer of interest.

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CONCLUSIONS Platinum allenylphosphonium complexes have been generated via a metal-mediated isomerization of the propargylphosphonium ligand. Initial coordination via the terminal CC group of the allene is observed, but thermal isomerization generates an equilibrium mixture of the terminally and internally coordinated complexes. A recurrent feature to emerge from the coordination of the propargylic salt was the facile rearrangement to the allenyl isomer. This can be rationalized with recourse to computational studies on the free phosphonium salts which suggest that the allenyl form is a more effective π-acceptor than the propargyl isomer. Calculations also show that the α-alkynyl form is thermodynamically the most stable isomer in the gas phase, suggesting that the isomerization [1]+ → [3]+ might in principle be catalyzed by a suitable transition-metal center, depending on the strength of [3] + coordination. Generation of an alkynylphosphonium complex is possible, but rearrangement of [2]+ to [3]+ does not occur within the platinum coordination sphere. Ongoing investigations into group 9 chemistry are underway.

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EXPERIMENTAL SECTION

General Considerations. All manipulations of air-sensitive compounds were carried out under a dry and oxygen-free nitrogen atmosphere using standard Schlenk, vacuum-line, and inert-atmosphere (argon) drybox techniques with dry and degassed solvents. Once isolated, the products were generally air stable both as solids and in solution. NMR spectra were recorded at 25 °C on a Varian Mercury 300 (1H at 300.1 MHz, 31P at 121.5 MHz), Varian Inova 300 (1H at 299.9 MHz, 13C at 75.47 MHz, 31P at 121.5 MHz, 195Pt at 64.53 MHz), Varian Mercury 400 (1H at 399.9 MHz, 13C at 100.5 MHz, 31P at 161.9 MHz), Varian Inova 500 (1H at 500.0 MHz, 13C at 125.7 MHz, 31P at 202.4 MHz), and Bruker Avance 600 (1H at 600.0 MHz, 13 C at 150.9 MHz) spectrometers. Chemical shifts (δ) are reported in ppm and referenced to the residual protonated solvent peak (1H, 13C), external 85% H3PO4 (31P), or external K2[PtCl6] (195Pt) with coupling 4771

dx.doi.org/10.1021/om400406s | Organometallics 2013, 32, 4766−4774

Organometallics

Article

14.5543(6) Å, β = 98.377(2)°, V = 2209.33(16) Å3, Z = 4, ρcalcd = 1.44 Mg m−3, μ(Mo Kα) = 0.26 mm−1, T = 200(2) K, colorless plate, 0.46 × 0.29 × 0.12 mm, 3886 independent reflections. F2 refinement, R = 0.055, Rw = 0.149 for 3309 reflections (I > 2σ(I), 2θmax = 55°), 280 parameters. Synthesis of [Ph3PCH2C(CH2)OC(CH3)CHPPh3](PF6)2 ([5](PF6)2). Crude [1]PF6 (2.656 g, 5.951 mmol) was dissolved in hot THF (ca. 30 mL, 50 °C) and gravity-filtered to remove insoluble impurities. Distilled water was added until the solution became cloudy (ca. 20 mL). The solution was cooled, resulting in a brown oil and white crystals. The THF was removed under reduced pressure, and the water was decanted off the solid. Hot methanol (ca. 50 °C) was added to dissolve the brown oil; however, some of the white crystals remained insoluble. This solution was cooled and allowed to crystallize, resulting in a mixture of brown and white crystals that were collected by vacuum filtration. The brown and white crystals appear to be two different crystal forms of [5](PF6)2 that provide the same spectroscopic data when dissolved. Yield: 0.206 g (0.226 mmol, 8%). The remaining starting material was recovered. IR (Nujol; ν/ cm−1): 1629 (CC); 1440 (PCH2); 1110 (PPh); 836 (PF6). IR (CH2Cl2; ν/cm−1): 1619 (CC); 1440 (PCH2); 1111 (PPh); 846 (PF6). 1H NMR (CD3CN; δ/ppm): 7.88−7.45 (m, 30H, C6H5); 5.94 (dd, 1H, PCH, 2JPH = 15.2, 4JHH = 0.8); 4.27 (d, 1H, CCH2, 4JPH = 3.9); 4.26 (d, 1H, CCH2, 4JPH = 4.0); 3.86 (d, 2H, PCH2, 2JPH = 15.2); 1.93 (s, 3H, CH3, resonance partially obscured by the residual solvent peak (quintet at 1.94 ppm), confirmed by a 1H−1H COSY NMR experiment). 13C{1H} NMR (CD3CN; δ/ppm): 174.9 (d, 2JPC = 4.6); 146.1 (d, 2JPC = 11.5); 136.6 (d, C4(PPh3), 4JPC = 3.4); 135.9 (d, C4(PPh3), 4JPC = 3.4); 134.9 (d, C2,3,5,6(PPh3), JPC = 10.4); 134.5 (d, C2,3,5,6(PPh3), JPC = 11.5); 131.3 (d, C2,3,5,6(PPh3), JPC = 2.3); 131.1 (d, C2,3,5,6(PPh3), JPC = 3.4); 120.5 (d, C1(PPh3), 1JPC = 92.1); 118.0 (d, C1(PPh3), 1JPC = 87.4); 106.7 (d, =CH2, 3JPC = 8.1); 91.0 (d, PCH, 1 JPC = 94.4); 29.5 (d, PCH2, 1JPC = 51.8); 20.1 (d, CH3, 3JPC = 11.5). 31 1 P{ H} NMR (CD3CN; δ/ppm): 19.7 (s); 11.4 (s); −144.6 (sep, PF6, 1JPF = 707.0). MS-ESI(+): m/z 783.8 [M − PF6 + H2O]+, 765.6 [M − PF6]+, 619.7 [M − H]+, 310.6 [M − 2PF6]2+, 301.5 [Ph3PC3H3]+. Accurate mass: found 765.2038 [M − PF6]+, calcd for C42H38F6OP3: 765.2040. Anal. Found: C, 55.45; H, 4.32; N, 0.00. Calcd for C42H38F12OP4: C, 55.40; H, 4.21; N, 0.00. Crystal data for C42H38OP2·2PF6: Mw = 910.63, orthorhombic, Pbc21, a = 10.8056(2) Å, b = 15.8370(2) Å, c = 24.4050(3) Å, V = 4176.39(11) Å3, ρcalcd = 1.45 Mg m−3, Z = 4, μ(Mo Kα) = 0.27 mm−1, T = 200(2) K, orange block, 0.41 × 0.34 × 0.25 mm, 7336 independent reflections. F2 refinement, R = 0.037, Rw = 0.088 for 6449 reflections (I > 2σ(I), 2θmax = 50°), 640 parameters. Synthesis of [Pt(η2-CH2CCHPPh3)(PPh3)2]PF6 ([6]PF6). A mixture of [Pt(C2H4)(PPh3)2] (100 mg, 0.134 mmol) and [1]PF6 (60 mg, 0.13 mmol) in THF (8 mL) was stirred for 24 h. At t = 5 minutes, all [1]PF6 had been consumed with the formation of an intermediate presumed to be the β-alkynylphosphonium complex [Pt(η2-HC CCH2PPh3)(PPh3)2]+ giving rise to the three resonances at δP = 21.83 (CH2P, JPP = 30.1, 3.1), 26.37 (JPP = 28.2, 3.1) and 27.55 (JPP = 29.1 Hz) though this species could not be isolated. The solution was concentrated to ca. 2 mL under reduced pressure, and the beige product was precipitated by addition of n-hexane, collected by filtration, and washed with hexane. Crystals suitable for crystallographic analysis were obtained by slow diffusion of benzene into a solution of [6]PF6 in CH2Cl2. Yield: 0.143 g (0.123 mmol, 92%). IR (Nujol; ν/cm−1): 1436 (PC), 1110 (PPh), 837 (PF6). IR (CH2Cl2; ν/ cm−1): 1437 (PC), 1110 (PPh), 846 (PF6). 1H NMR (CDCl3; δ/ ppm): 7.81−6.85 (m, 45H, C6H5); 5.37 (dddt, 1H, PCH, 2JPH = 33.6, trans-4JPH = 12.8, cis-4JPH = 1.8, 4JHH = 2.6, 3JPtH = 77.0); 1.49 (m, 2H, PtCH2, 2JPtH = 59.2). 13C{1H} NMR (CDCl3; δ/ppm): 197.9 (ddd,  C, CPPh3-2JPC = 9.4, cis-2JPC = 4.3, trans-2JPC = 60.1); 134.6 (d, C4(CPPh3), 4JPC = 3.1); 133.8 (d, C2,3,5,6(PtPPh3), JPC = 13.7); 133.7 (d, C2,3,5,6(PtPPh3), JPC = 13.7); 133.4 (d, C2,3,5,6(CPPh3), JPC = 9.4); 130.1 (d, C4(PtPPh3), JPC = 2.1); 130.0 (d, C4(CPPh3), JPC = 2.1); 130.0 (d, C2,3,5,6(CPPh3), JPC = 12.7); 128.2 (d, C2,3,5,6(PtPPh3), JPC = 10.6); 128.2 (d, C2,3,5,6(PtPPh3), JPC = 10.6); 120.2 (d, C1(CPPh3),

JPC = 95.9). 31P{1H} NMR (CDCl3; δ/ppm): 18.9 (s, PPh3); −143.7 (sep, PF6, 1JPF = 712.7). 31P{1H} NMR (CD3CN; δ/ppm): 18.4 (s, PPh3); −144.6 (sep, PF6, 1JPF = 707.9). MS-ESI(+): m/z 301.3 [M − PF6]+. Accurate mass: found 301.1145 [M − PF6]+, calcd for C21H18P 301.1146. Anal. Found: C, 56.50; H, 3.98; N, 0.00. Calcd for C21H18F6P2: C, 56.51; H, 4.06; N, 0.00. Crystal data for C21H18P·PF6: Mw = 446.29, monoclinic, P21/n, a = 14.9733(7) Å, b = 8.2751(4) Å, c = 16.2645(7) Å, β = 92.443(2)°, V = 2013.43(16) Å3, Z = 4, ρcalcd = 1.47 Mg m−3, μ(Mo Kα) = 0.28 mm−1, T = 150(2) K, colorless block, 0.22 × 0.16 × 0.11 mm, 3529 independent reflections. F2 refinement, R = 0.038, Rw = 0.103 for 2841 reflections (I > 2σ(I), 2θmax = 50°), 342 parameters. Synthesis of [Ph3PCCCH3]Br ([3]Br). The title compound was synthesized according to the literature procedure.2 Yield: 1.302 g (3.415 mmol, 65%). IR (Nujol; ν/cm−1): 2206 (CC); 1440 (PC); 1112 (PPh). IR (CH2Cl2; ν/cm−1): 2214 (CC); 1440 (PC); 1112 (PPh).1H NMR (CDCl3; δ/ppm): 7.85−7.66 (m, 15H, C6H5); 2.56 (d, 3H, CH3, 4JPH = 4.4). 1H NMR (CD3CN; δ/ppm): 7.91−7.71 (m, 15H, C6H5); 2.44 (d, 3H, CH3, 4JPH = 4.4). 13C{1H} NMR (CD3CN; δ/ppm): 136.5 (d, C4(PPh3), 4JPC = 3.1); 134.2 (d, C2,3,5,6(PPh3), JPC = 12.5); 131.6 (d, C2,3,5,6(PPh3), JPC = 14.1); 123.0 (d, PCC, 2JPC = 33.5); 119.6 (d, C1(PPh3), 1JPC = 100.4); 60.7 (d, P-CC, 1JPC = 193.1); 6.6 (s, CH3). 31P{1H} NMR (CDCl3; δ/ppm): 6.1 (s, PPh3). 31 1 P{ H} NMR (CD3CN; δ/ppm): 5.2 (s, PPh3). MS-ESI(+): m/z 301.3 [M − Br]+. Accurate mass: found 301.1155 [M − Br]+, calcd for C21H18P 301.1146. Synthesis of [Ph3PCCCH3]PF6 ([3]PF6). Solid NaPF6 (0.184 g, 1.10 mmol) was added to a solution of [3]Br (0.207 g, 0.543 mmol) in distilled water (10 mL). The product ([3]PF6) formed immediately as a white precipitate, which was collected by vacuum filtration, washed thoroughly with H2O, and dried under high vacuum. Yield: 0.218 g (0.488 mmol, 90%). IR (Nujol; ν/cm−1): 2211 (CC); 1440 (PC); 1113 (PPh); 836 (PF6). IR (CH2Cl2; ν/cm−1): 2214 (CC); 1440 (PC); 1113 (PPh); 845 (PF6). 1H NMR (CDCl3; δ/ppm): 7.86−7.71 (m, 15H, C6H5); 2.48 (d, 3H, CH3, 4JPH = 4.8). 1H NMR (CD3CN; δ/ ppm): 7.91−7.71 (m, 15H, C6H5); 2.41 (d, 3H, CH3, 4JPH = 4.8). 13 C{1H} NMR (CD3CN; δ/ppm): 136.7 (d, C4(PPh3), 4JPC = 3.2); 134.4 (d, C2,3,5,6(PPh3), JPC = 12.9); 131.4 (d, C2,3,5,6(PPh3), JPC = 14.2); 123.0 (d, PCC, 2JPC = 33.0); 119.8 (d, C1(PPh3), 1JPC = 100.2); 60.8 (d, PCC, 1JPC = 192.7); 6.4 (d, CH3, 3JPC = 3.9). 31 1 P{ H} NMR (CDCl3; δ/ppm): 6.1 (s, PPh3); −143.7 (sep, PF6, 1JPF = 712.1). 31P{1H} NMR (CD3CN; δ/ppm): 5.5 (s, PPh3); −144.5 (sep, PF6, 1JPF = 706.7). MS-ESI(+): m/z 301.4 [M − PF6]+. Accurate mass: found 301.1146 [M − PF6]+, calcd for C21H18P 301.1146. Anal. Found: C, 56.63; H, 4.00; N, 0.00. Calcd for C21H18F6P2: C, 56.51; H, 4.06; N, 0.00. Synthesis of [Ph3PCH2C(CH2)OCH3]PF6 ([4]PF6). Crude [1]PF6 (2.45 g, 5.50 mmol) was dissolved in hot methanol (ca. 60 mL, 50 °C), and the solution was decanted to remove the insoluble impurities. The solution was cooled, and the white crystals that formed were collected by vacuum filtration and washed with a small amount of methanol. Yield: 0.370 g (0.774 mmol, 14%). The remaining product in solution was shown by 1H and 31P{1H} NMR spectroscopy to be [2]PF6. IR (Nujol; ν/cm−1): 1629 (CC); 1440 (PCH2); 1110 (PPh); 838 (PF6). IR (CH2Cl2; ν/cm−1): 1619 (CC); 1440 (PCH2); 1111 (PPh); 846 (PF6). 1H NMR (CDCl3; δ/ppm): 7.85− 7.60 (m, 15H, C6H5); 4.35 (apparent t, 1H, CCH, J = 3.6); 4.15 (1H, CCH, coupling and multiplicity obscured by overlapping PCH2 resonance); 4.13 (d, 2H, PCH2, 2JPH = 14.4); 3.25 (s, 3H, OCH3). 13C{1H} NMR (CD3CN; δ/ppm): 155.6 (d, =C−O, 2JPC = 10.3); 136.0 (d, C4(PPh3), 4JPC = 2.3); 134.8 (d, C2,3,5,6(PPh3), JPC = 9.2); 130.9 (d, C2,3,5,6(PPh3), JPC = 13.8); 119.2 (d, C1(PPh3), 1JPC = 87.5); 89.8 (d, =CH2, 3JPC = 9.2); 56.0 (s, OCH3); 31.3 (d, PCH2, 1JPC = 51.7). 31P{1H} NMR (CDCl3; δ/ppm): 12.9 (s, PPh3); −144.4 (sep, PF6, 1JPF = 712.2). MS-ESI(+): m/z 333.3 [M − PF6]+. Accurate mass: found 333.1408 [M − PF6]+, calcd for C22H22OP 333.1408. Anal. Found: C, 55.39; H, 4.65; N, 0.00. Calcd for C22H22F6OP2: C, 55.24; H, 4.64; N, 0.00. Crystal data for C22H22OP·PF6: Mw = 487.35, monoclinic, P21/n, a = 13.0623(5) Å, b = 11.7465(5) Å, c = 1

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Organometallics

Article

133.2 (d, C2,3,5,6(PPh3), JPC = 10.6); 130.3 (s, C4(PPh3)); 130.1 (s, C 4(PPh3)); 129.8 (d, C2,3,5,6(PPh3), J PC = 12.7); 128.4 (d, C2,3,5,6(PPh3), JPC = 10.2); 128.1 (d, C2,3,5,6(PPh3), JPC = 10.0); 121.9 (dd, C1(PPh3), 1JPC = 91.3, JPC = 2.0); 91.7 (ddd, P-CC, 1JPC = 88.9, trans-2JPC = 73.2, cis-2JPC ≈ 5); 12.3 (dd, CH3, trans-3JPC = 9.3, 3 JPC = 6.0). The C1(PtPPh3) resonances could not be unequivocally assigned. 31P{1H} NMR (CDCl3; δ/ppm): 24.4 (dd, PtPPh3, 2JPP = 17.6, cis-3JPP = 33.5, 1JPtP = 3270); 24.0 (dd, PtPPh3, 2JPP = 17.6, trans-3JPP = 61.5, 1JPtP = 4024); 0.9 (dd, CPPh3, trans-3JPP = 61.5, cis-3JPP = 33.5, 2JPtP = 33.4); −143.6 (sep, PF6, 1JPF = 712.6). 195Pt NMR (CDCl3; δ/ppm): −4598 (ddd, Pt, 1JPtP = 4026, 1JPtP = 3272, 2 JPtP = 35.7). MS-ESI(+): m/z 1020.7 [M]+. Accurate mass: found 1020.2635 [M]+, calcd for C57H48P3195Pt 1020.2617. Anal. Found: C, 54.82; H, 4.18; N, 0.00. Calcd for C57H48F6P4Pt·CHCl3: C, 54.20; H, 3.84; N, 0.00. Crystal data for C57H48P3Pt·PF6·CHCl3: Mw = 1285.36, triclinic, P1̅ (No. 2), a = 10.7392(2) Å, b = 15.2057(2) Å, c = 17.1417(2) Å, α = 81.3680(9)°, β = 74.9346(8)°, γ = 82.5148(7)°, V = 2660.13(7) Å3, Z = 2, ρcalcd = 1.605 Mg m−3, μ(Mo Kα) = 2.968 mm−1, T = 200(2) K, colorless block, 0.11 × 0.15 × 0.25 mm, 15526 independent reflections. F2 refinement, R = 0.0426, Rw = 0.100 for 12700 reflections (I > 2σ(I), 2θmax = 60°), 649 parameters.

1

JPC = 87.5); 83.3 (ddd, PCH, 1JPC = 72.8, trans-3JPC = 11.0, cis-3JPC = 7.9); 14.0 (d, PtCH2, 2JPC = 43.3, JPC = 5.1). The C1(PtPPh3) resonances could not be unequivocally assigned. 31P{1H} NMR (CDCl3; δ/ppm): 32.5 (d, PtPPh3, 2JPP = 26.7, 1JPtP = 3354); 27.7 (dd, PtPPh3, 2JPP = 26.7, trans-4JPP = 55.4, 1JPtP = 3156); 15.1 (d, CPPh3, trans-4JPP = 55.4, 3JPtP = 297.6); −143.6 (sep, PF6, 1JPF = 712.4). 195Pt NMR (CDCl3; δ/ppm): 4684 (ddddt, Pt, 1JPtP = 3353, 1JPtP = 3146, 3 JPtP = 300.8, 3JPtH = 69.1, 2JPtH = 61.6). MS-ESI(+): m/z 1020.7 [M]+, 758.7 [M − PPh3]+. Accurate mass: found 1020.2650 [M]+, calcd for C57H48P3195Pt 1020.2617. Anal. Found: C, 58.57; H, 4.17; N, 0.00. Calcd for C57H48F6P4Pt: C, 58.72; H, 4.15; N, 0.00. Crystal data for C57H48P3Pt·PF6·0.15CH2Cl2: Mw = 1178.65, triclinic, P1̅ (No. 2), a = 12.673(10) Å, b = 14.815(10) Å, c = 15.954(12) Å, α = 65.82(3)°, β = 75.91(3)°, γ = 84.18(3)°, V = 2650(3) Å3, Z = 2, ρcalcd = 1.525 Mg m−3, μ(Mo Kα) = 2.88 mm−1, T = 149(2) K, light yellow plate, 0.12 × 0.08 × 0.03 mm, 7968 independent reflections. F2 refinement, R = 0.117, Rw = 0.298 for 3533 reflections (I > 2σ(I), 2θmax = 47°), 625 parameters. Synthesis of [Pt{η2-C(PPh3)CCH2}(PPh3)2]PF6 ([8]PF6). The title compound was obtained by heating a solution of [6]PF6 (8 mg, 7 μmol) in chloroform at 50 °C for 48 h and separated from residual [6]PF6 by crystallization from CH2Cl2 and toluene as a dichloromethane solvate. Yield: 5 mg (4 μmol, 60%). IR (Nujol; ν/ cm−1): 1437 (PC), 1109 (PPh), 837 (PF6). IR (CH2Cl2; ν/cm−1): 1437 (PC), 1110 (PPh), 846 (PF6). 1H NMR (CDCl3; δ/ppm): 7.81−6.86 (m, 45H, C6H5); 5.86 (m, 1H, E-CH2, 4JPH = 23.2, 2JPtH = 65.2, other couplings apparent but not resolved); 4.34 (m, 1H, Z-CH2, 4 JPtH = 44.0, other couplings apparent but not resolved); 3.42 (m, 1H, CH, 2JPtH = 60.0, other couplings apparent but not resolved). 13C{1H} NMR (CDCl3; δ/ppm): 158.4 (ddd, C, trans-2JPC = 66.4, cis-2JPC = 3.0, CPPh3-2JPC = 3.0); 134.3 (d, C1(PPh3), 1JPC = 43.8, JPtC = 20.4); 134.0 (d, C2,3,5,6(PPh3), JPC = 13.6); 133.8 (d, C4(PPh3), 4JPC = 3.0); 133.6 (d, C2,3,5,6(PPh3), JPC = 9.1); 133.1 (d, C2,3,5,6(PPh3), JPC = 12.7); 132.4 [dd, C1(PPh3), 1JPC = 50.4, JPC = 1.7, JPtC = 34.8); 130.5 (d, C4(PPh3), 4JPC = 1.4); 130.4 (d, C4(PPh3), 4JPC = 1.2); 129.7 (d, C2,3,5,6(PPh3), JPC = 12.1); 128.7 (d, C2,3,5,6(PPh3), JPC = 10.6); 128.3 (d, C2,3,5,6(PPh3), JPC = 10.6); 123.2 (dd, C1(PPh3), 1JPC = 87.5, JPC = 3.0, JPtC = 20.5); 103.7 (apparent dt, CH2, 3JPC = 8.7, 3JPC = 2.5); 2.8 (dd, PCH, 1JPC = 54.3, 2JPC = 6.0). 31P{1H} NMR (CDCl3; δ/ppm): 28.8 (dd, PtPPh3, 2JPP = 20.9, cis-3JPP = 3.9, 1JPtP = 4074); 25.0 (dd, PtPPh3, 2JPP = 20.9, trans-3JPP = 9.6, 1JPtP = 2902); 21.9 (dd, CPPh3, trans-3JPP = 9.6, cis-3JPP = 3.9, 2JPtP = 110.4); −143.6 (sep, PF6, 1JPF = 712.4). The low solubility and propensity to crystallize precluded acquisition of 195Pt NMR data. MS-ESI(+): m/z 1020.7 [M]+, 758.6 [M − PPh3]+. Accurate mass: found 1020.2618 [M]+, calcd for C57H48P3195Pt 1020.2617. Anal. Found: C, 54.65; H, 4.04; N, 0.00. Calcd for C57H48F6P4Pt·1.5CH2Cl2: C, 54.33; H, 3.97; N, 0.00. Crystal data for C57H48P3Pt·PF6·1.5CH2Cl2: Mw = 1293.38, triclinic, P1̅ (No. 2), a = 10.4806(1) Å, b = 12.4260(2) Å, c = 21.6032(3) Å, α = 91.5089(6)°, β = 90.8490(9)°, γ = 105.0660(8)°, V = 2715.09(6) Å3, Z = 2, ρcalcd = 1.582 Mg m−3, μ(Mo Kα) = 2.91 mm−1, T = 200(2) K, colorless plate, 0.49 × 0.34 × 0.09 mm, 12392 independent reflections. F2 refinement, R = 0.028, Rw = 0.067 for 11211 reflections (I > 2σ(I), 2θmax = 55°), 658 parameters. Synthesis of [Pt{η2-C(CH3)CPPh3}(PPh3)2]PF6 ([9]PF6). A mixture of [Pt(C2H4)(PPh3)2] (149 mg, 0.199 mmol) and [3]PF6 (89 mg, 0.20 mmol) in CH2Cl2 (8 mL) was stirred overnight. The reaction mixture was filtered, and toluene (ca. 2 mL) was added. The solution was concentrated under reduced presure to precipitate the product as a white powder, which was collected by filtration and washed with Et2O. Crystals of a chloroform solvate suitable for crystallographic and elemental analysis were obtained by slow diffusion of benzene into a solution of [9]PF6 in CH2Cl2/CHCl3. Yield: 0.210 g (0.180 mmol, 91%). IR (Nujol; ν/cm−1): 1679 (CC), 1435 (PC), 1108 (PPh), 835 (PF6). IR (CH2Cl2; ν/cm−1): 1690 (CC), 1437 (PC), 1110 (PPh), 846 (PF6). 1H NMR (CDCl3; δ/ppm): 7.66−6.84 (m, 45H, C6H5); 1.42 (dd, 3H, CH3, 4JPH = 7.5, 4JPH = 3.4, 3JPtH = 25.8). 13C{1H} NMR (CDCl3; δ/ppm): 172.0 (dd, P−CC, trans-2JPC = 65.3, 2JPC = 3.6); 134.1 (d, C4(PPh3), 4JPC = 2.9); 134.0 (d, C2,3,5,6(PPh3), JPC = 13.1); 133.9 (d, C2,3,5,6(PPh3), JPC = 12.3);

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ASSOCIATED CONTENT

S Supporting Information *

CIF files giving crystallographic data for [1]PF6 (CCDC 932235), [2]PF6 (CCDC 932236), [4]PF6 (CCDC 932237), [5]PF6 (CCDC 932238), [6]PF6 (CCDC 932239), [8]PF6 (CCDC 932240), and [9]PF6 (CCDC 932241) and tables giving computational details. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for A.F.H.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Australian Research Council (DP110101611). REFERENCES

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