Homo- and Heteropolynuclear Complexes Containing Bidentate

Apr 29, 2016 - The buried volumes (%Vbur) and Tolman cone angles for representative 4-phosphino-NHCs calculated from structural data are compared to ...
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Homo- and Heteropolynuclear Complexes Containing Bidentate Bridging 4‑Phosphino-N-Heterocyclic Carbene Ligands Zeyu Han, Joshua I. Bates, Dominik Strehl, Brian O. Patrick, and Derek P. Gates* Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1 S Supporting Information *

ABSTRACT: The abnormal reaction of phosphaalkenes with N-heterocyclic carbenes (NHC) offers a convenient method to introduce new functionality at the backbone of an NHC. The 4phosphino-substituted NHC (1a) derived from 1,3-dimesitylimidazol-2-ylidene (IMes) and MesPCPh2 is shown to be an effective bifunctional ligand for Au(I) and Pd(II). Several new complexes are reported: 2a: 1a·AuCCl, 3a: 1a·(AuCl)2, 4a: [(1a)2AuC]Cl, 5a: [(1a·AuPCl)2AuC]Cl], and 6a: 1a·(PdC) (AuPCl). The reaction of 4-phosphino-NHC 1b, derived from 1,3-di(cyclohexyl)imidazol-2-ylidene (ICy) and MesPC(4C6H4F)2, with (tht)AuCl (2 equiv, tht = tetrahydrothiophene) affords the fascinating tetranuclear 5b [(1b·AuPCl)2AuC][AuCl2]. The molecular structure of 5b features a close Au···Au contact (3.0988(4) Å) between the bis(carbene)gold(I) cation and the dichloroaurate(I) anion. The buried volumes (%Vbur) and Tolman cone angles for representative 4-phosphino-NHCs calculated from structural data are compared to related carbenes and phosphines. The molecular structures are reported for complexes 3a, 4a, 5b, and 6a.

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backbone (i.e., E1 or E2) is relatively rare. Notable examples include functionalizing the backbone with deuterium,9a halogens,9b,c lithium,9d boron,9e−g nitrogen,9h,i oxygen,9j,k silicon,9l−n and sulfur.9o In 2009, we discovered the abnormal reaction of an NHC (1,3-dimesitylimidazol-2-ylidene, or IMes) with a phosphaalkene (PA) to afford the first 4-phosphino-substituted NHC (IMesP) (Scheme 1, 1a: R = Ar = Mes; R′ = R″ = Ph).10−12 P-

INTRODUCTION Although the ligand properties of N-heterocyclic carbenes (NHCs) have been studied since the 1960s, the last two decades have witnessed the widespread application of isolable NHCs as ligands for homogeneous catalysis.1,2 An attractive feature of NHCs is their strong σ-electron-donating properties,3 which leads to very strong NHC−metal bonds4 and prevents decomposition of the catalysts. Although the donor properties of NHCs are readily modified either by changing the Nsubstituent adjacent to the carbene center5 or through annulation of imidazole with an aromatic ring, 6 the modification of the backbone substituents with heteroatoms (Chart 1, I) is particularly desirable since the backbone functionalities can have a profound impact on the electronic and catalytic properties of NHCs.7,8 As a consequence of synthetic challenge, the incorporation of heteroatoms at the

Scheme 1. Abnormal Reaction of an NHC with a Phosphaalkene to Afford a 4-Phosphino-NHC (1)

Chart 1. NHCs Bearing Functional Group(s) (E1, E2) at the C4 and/or C5 Positions (I) and Their Dinuclear 4Phosphino-Substituted Complexes II and IIIa

Functional NHCs are of interest because they offer both an additional binding site and an opportunity to modify the donor properties of the carbene center. Additional examples include the 4-phosphino-substituted NHCs of Bertrand and coworkers,13 4,5-diphosphino-substituted NHCs of Ruiz and coworkers,14 and 4-phosphanido-substituted NHCs of Streubel, Nyulaszi, and Gates.15 The incorporation of phosphorus at the backbone of an NHC has facilitated the synthesis of novel Received: March 18, 2016

a 1

R , R2 = alkyl/aryl groups. © XXXX American Chemical Society

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DOI: 10.1021/acs.inorgchem.6b00686 Inorg. Chem. XXXX, XXX, XXX−XXX

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the 13C{1H} NMR spectrum revealed that the signal assigned to the carbenic carbon (δ = 175.2 in THF) was similar to that observed for complex 3a (δ = 177.6) and significantly upfield from that of the free carbene (δ = 220.3). Although these observations are consistent with the formation of complex 2a, we have been unable to isolate a pure material or obtain single crystals suitable for X-ray diffraction to confirm this. Altering the reaction stoichiometry leads to some novel products. For example, employing a 1:2 ratio of (tht)AuCl to NHC 1a afforded, within minutes, a colorless precipitate from THF. Analysis of a CH2Cl2 solution of the precipitate by 31P NMR spectroscopy revealed a singlet resonance at −37.8 ppm. This observation was consistent with a single product containing an uncoordinated phosphine. Further information on the nature of the product was obtained from the 13C{1H} NMR spectrum, which showed a single resonance in the carbene region (δC = 186.5). On the basis of the 2:1 ratio of (tht)AuCl to 1a, these data suggest that the product is bis(IMesP)gold(I) salt 4a (Scheme 3). Assuming this is the

homo- and heteropolynuclear complexes (e.g., Chart 1, II and III).10,11,14,16 Herein, we report on the coordination chemistry of 4phosphino-NHCs prepared from the abnormal reaction of NHCs and phosphaalkenes. In particular, we have isolated and structurally characterized novel complexes of gold(I) and/or palladium(II) that highlight the interesting bidentate bridging behavior of these ligands.

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RESULTS AND DISCUSSION Gold(I) Complexes of IMesP and ICyP. Gold(I) was chosen for coordination studies due to its tendency to form stable complexes with both carbenes and phosphines. Treating a THF solution of 1a with (tht)AuCl (2 equiv, tht = tetrahydrothiophene) afforded the digold complex 3a quantitatively by 31P NMR spectroscopy, which was isolated in moderate yield (55%) after recrystallization (Scheme 2). The Scheme 2. Synthesis of Gold(I) Complexes 2a and 3a

Scheme 3. Synthesis of bis(IMesP)gold(I) Salts 4a and 5a

downfield shift of the phosphine resonance (3a: δP = −0.1 vs 1a: δP = −37.9) and upfield shift of the carbene resonance (3a: δC = 177.6 vs 1a: δC = 220.3) are consistent with coordination of both the carbene and phosphine moieties of 1a. For comparison, similar spectroscopic changes are observed for the related Mes(Me)P-CPh2H [Mes(Me)(AuCl)P-CPh2H: δP = 16.0 versus Mes(Me)P-CPh2H: δP = −23.0]17 and IMes [IMes· AuCl: δC = 173.4 versus IMes: δC = 220.3].18 The coordination of two AuCl moieties was confirmed by X-ray crystallographic analysis, and the molecular structure of 3a is shown in Figure 1. To determine whether the phosphine or the carbene binds gold(I) first, IMesP 1a and (tht)AuCl (1 equiv) were mixed in THF solution. Analysis of the reaction mixture by 31P NMR spectroscopy revealed a singlet resonance at −36.4 ppm. The chemical shift, being similar to 1a (δ = −37.3 in THF), suggests minimal change in the phosphorus environment. In addition,

case, the NMR data suggest that only a single diastereomer is present. X-ray crystallography determined this to be the R,R and S,S enantiomeric pair (Figure 2). The closest contact between the Cl anion and an H atom of the Ph (H27) is 2.897(2) Å, which is slightly less than the sum of the van der Waals radii (ca. 2.9 Å). Although salts of the form [(NHC)2Au]X have been isolated and characterized,19 a salt

Figure 2. Molecular structure of the cation in 4a·2CH2Cl2·H2O (thermal ellipsoids set at 50% probability). The solvate and all hydrogen atoms are omitted for clarity.

Figure 1. Molecular structure of 3a (thermal ellipsoids set at 50% probability). The solvate atoms and all hydrogen atoms are omitted for clarity. B

DOI: 10.1021/acs.inorgchem.6b00686 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry containing the [(IMes)2Au]+ cation has not been isolated and has only been detected by mass spectrometry.20 Gold(I) complex 4a, possessing two free phosphine moieties, reacts with (tht)AuCl (2 equiv) to afford a new compound tentatively assigned as 5a (Scheme 3). Analysis of the product by 31P{1H} NMR spectroscopy was consistent with this assignment; however two signals are observed in the region expected for a P−Au(I) moiety rather than one (δP = 0.6 and 0.5). The presence of two signals may be a consequence of stereo or rotational isomerism. Unfortunately, crystals suitable for X-ray crystallographic analysis could not be obtained for the species. However, support for this assignment was obtained from related work involving 1b, which was obtained from the abnormal reaction of ICy (1,3-di(cyclohexyl)imidazol-2-ylidene) with MesPC(4-C6H4F)2. Compound 1b was treated with (tht)AuCl (1 equiv) in THF followed by further addition of (tht)AuCl (1 equiv) to obtain a single product (Scheme 4).

A heterodinuclear complex has also been obtained with a 4phosphino-NHC ligand. For example, compound 1a was treated with Pd(cod)Cl2 (1 equiv) in THF to afford the NHC-Pd(II) complex as an intermediate as judged by its 31P NMR chemical shift (δ = −38.8) being close to 1a (δ = −37.3). Although we did not isolate this species, the subsequent addition of (tht)AuCl (1 equiv) afforded a single product (31P NMR: δ = −1.0). X-ray crystallographic analysis of single crystals obtained from the reaction mixture identified the product as the dinuclear compound 6a (Figure 4, Scheme 5). Compound 6a was also characterized by 1H NMR spectroscopy, mass spectrometry, and elemental analysis.

Scheme 4. Synthesis of Tetranuclear Complex 5b

Analysis of the reaction mixture by 31P NMR spectroscopy revealed a signal at 0.2 ppm suggesting phosphine−gold(I) coordination. X-ray crystallographic analysis of single crystals obtained from the reaction mixture identified the product as the fascinating tetragold(I) compound 5b (Figure 3). Remarkably,

Figure 4. Molecular structure of 6a·CH2Cl2 (thermal ellipsoids set at 50% probability). The solvate atoms and all hydrogen atoms are omitted for clarity.

Scheme 5. Synthesis of Heterodinuclear Complex 6a

Molecular Structures and Buried Volume of IMesP and ICyP. Details of the crystal structure determinations undertaken in the present study are given in Table 1, and important metrical parameters for the new NHCs and their complexes are given in Table 2. For the most part, the bond lengths within the C3N2 ring do not change considerably upon coordination to gold(I) or palladium(II). The Au(2)−C(2) bond in 3a [1.971(5) Å] is slightly shorter than that found in 4a and 5b [range: 2.007(4)−2.014(4) Å] and is comparable to IMes−AuCl [1.999(5) Å]. The P(1)−Au(1) [2.238(1) Å] and Au(2)−Cl(2) [2.284(1) Å] bonds in 3a are both shorter than those found in the related Mes(Me)(AuCl)P−CPh2H [P−Au: 2.257(1) Å; Au−Cl: 2.305(1) Å],17 but are within the range observed in other phosphine−AuCl complexes [P−Au: 2.21− 2.26 Å; Au−Cl: 2.23−2.31 Å].24 In 6a, the Pd(1)−C(2) bond [1.996(6) Å] is close to that observed for the related complex trans-[IMes−PdCl2(py)] [1.969(2) Å].25 The angles within the C3N2 ring show subtle changes upon coordination to gold(I). Of note are the N−C−N angles, which

Figure 3. Molecular structure of 5b·2Et2O (thermal ellipsoids set at 50% probability). The solvate and all hydrogen atoms are omitted for clarity.

5b is C2 symmetric, with a close Au···Au contact (3.0988(4) Å) between the central gold(I) and the [AuCl2]− anion serving as the principal axis. Aurophilic interactions between gold(I) centers typically fall in the range 2.7−3.3 Å.21 For comparison, the related complex, ICyAuCl, does not disproportionate to [(NHC)2Au][AuCl2].18 The only gold(I)−carbene complex that forms such a salt structure is [(CAAC)2Au][AuCl2] [CAAC = cyclic (alkyl)(amino)carbene]. However, in contrast to 5b, this species does not show aurophilic interactions in the solid state (Au···Au > 7.4 Å).22 It should be noted that analogous silver(I)−carbene complexes are known to disproportionate and the NHCAgX (X = halogen) form can exist in equilibrium with the [(NHC)2Ag][AgX2].23 C

DOI: 10.1021/acs.inorgchem.6b00686 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Crystallographic Data for Compounds 3a, 4a, 5b, and 6a formula fw cryst syst space group Z a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) T (K) μ(Mo Kα) (cm−1) cryst size (mm3) dcalcd (Mg m−3) 2θ(max) (deg) no. reflns no. unique reflns R(int) refln/param ratio R1a [I > 2σ(I)] wR2 (all data)b GOF CCDC no. a

3a·CH2Cl2

4a·2CH2Cl2·H2O

5b·2Et2O

6a·CH2Cl2

C44H47Au2Cl4N2P 1170.54 monoclinic P21/c 4 15.736(1) 17.923(1) 16.645(1) 90 113.592(1) 90 4302.1(3) 173 71.31 0.8 × 0.4 × 0.1 1.807 55.8 30 967 10 277 0.0449 20.93 0.0344 0.0891 1.016 748236

C88H96AuCl3N4OP2 1661.84 monoclinic P21/n 4 17.381(1) 26.341(2) 18.497(1) 90 108.149(2) 90 8047.2(11) 100 20.82 0.25 × 0.1 × 0.1 1.372 49.4 59 370 13 713 0.0372 14.78 0.0363 0.0964 1.104 869366

C82H104Au4Cl4F4N4O2P2 2245.30 monoclinic C2/c 4 21.819(1) 16.899(1) 22.460(1) 90 91.469(1) 90 8278.8(9) 90 72.90 0.06 × 0.12 × 0.15 1.801 56.6 61 882 12 198 0.045 24.59 0.0330 0.0822 1.043 869367

C49H57AuCl7N2PPdS 1288.51 monoclinic P21/n 4 14.499(2) 20.544(2) 18.153(2) 90 108.275(3) 90 5134.4(9) 90 36.76 0.13 × 0.12 × 0.09 1.667 61.2 62 831 15 733 0.0525 25.25 0.0509 0.1344 1.081 1412922

R1 = ∑∥Fo| − |Fc∥/∑|Fo|. bwR2(F2 [all data]) = {∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]}1/2.

Table 2. Selected Metrical Parameters for IMes,a 1a,b and the New Compounds Prepared in This Study Bond Lengths (Å) C(2)−N(1) C(2)−N(2) N(2)−C(3) C(3)−C(4) C(4)−N(1) M(2)−C(2) M(1)−Cl(1) M(1)−P(1) M(2)−Cl(2) M(2)−M(3) Bond Angles (deg) C2−N1−C4 N1−C2−N2 C2−N2−C3 N2−C3−C4 N1−C4−C3 N1−C2−M1 N2−C2−M1 C2-M1−Cl1 P1−Au1−Cl1 C−Au−C a

IMes

1a

3a

4a

5b

6a

1.365(4) 1.371(4) 1.378(4) 1.331(5) 1.381(4)

1.363(2) 1.366(3) 1.406(2) 1.349(3) 1.388(2)

1.360(7) 1.345(6) 1.397(7) 1.354(7) 1.376(7) 1.971(5) 2.266(2) 2.238(1) 2.284(1)

1.351(8) 1.346(8) 1.405(8) 1.356(9) 1.388(8) 2.007(4) 2.010(4)

1.349(5) 1.351(5) 1.397(5) 1.360(5) 1.377(5) 2.014(4) 2.283(1) 2.242(1)

1.351(7) 1.346(7) 1.402(7) 1.336(8) 1.394(7) 1.996(6) 2.290(2) 2.238(2)

3.0988(4) 112.8(3) 101.4(2) 112.8(3) 106.5(3) 106.5(3)

113.1(2) 101.2(2) 114.1(2) 104.4(2) 107.2(2)

110.2(4) 105.1(5) 111.5(4) 105.2(5) 108.0(5) 125.9(4) 128.7(4) 176.9(2) 171.9(1)

110.9(6) 105.1(6) 111.5(6) 105.3(6) 107.4(6) 126.7(4) 128.2(4)

110.6(3) 105.8(3) 110.3(3) 106.0(3) 107.2(3) 126.7(3) 127.4(3)

110.4(5) 105.1(5) 111.0(5) 106.0(5) 107.5(5) 127.2(4) 127.6(4)

170.21(4) 176.8(2)

171.1(6)

177.8(2)

See ref 41. bSee ref 11.

(3a), 1.5(6)° (4a), 0.7(4)° (5b), 0.4(4)° (6a)]. We note that Ir(I) complexes of IMes itself display a similar asymmetrical distortion upon binding the metal [ΔN−C‑M: 2.9(8)°].26 The P− Au−Cl and/or C−Au−C/Cl angles in 3a, 4a, 5b, and 6a all deviate significantly from linearity, with the P−Au−Cl being greatest [3a: P(1)−Au(1)−Cl(1): 171.9(1)°, 5b: P(1)−

increase upon complexation. The increase in N−C−N angle is accompanied by a slight contraction in C−N−C angle. Interestingly, a common feature in all the complexes is the asymmetric binding of 1a to gold(I). This is evident upon examining the N−C−M bond angle, which is larger on the side of the NHC closest to the 4-phosphino substituent [2.8(6)° D

DOI: 10.1021/acs.inorgchem.6b00686 Inorg. Chem. XXXX, XXX, XXX−XXX

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may result from the fact that the Tolman method considers one point for each substituent, whereas the buried volume accounts for the entire bulk of the ligand within the coordination sphere of the metal. For extremely bulky phosphines such as 1a, this can result in significant differences in cone angle whether determined using the Tolman’s method or extracted from % Vbur.

Au(1)−Cl(1): 170.21(4)°, 6a: P(1)−Au(1)−Cl(1): 171.1(1)°]. Similar, but less dramatic distortions are observed with related gold(I) complexes containing bulky and/or asymmetric carbenes18 and phosphines.17,27 The aforementioned structural data suggest that the novel phosphine-substituted NHCs synthesized herein are sterically hindered ligands whether binding through the phosphine or the carbene donor sites. The “buried volume” (%Vbur)28−30 has been employed as a quantitative method to compare the steric demand of NHC and phosphine ligands with the novel 4phosphino-NHCs described herein. Calculations were performed using the Salerno molecular buried volume calculation (SambVca) software and the X-ray crystallographic data.31 The results are shown in Table 3.

ligand (L)

C−Au

IMe ICy 1ae 1bd IMes ItBu CAAC IPr* PMe3 PPh3 PtBu3 PMes3

26.3 27.4 36.2 32.8 36.5 38.3 51.2 55.1

P−Au

57.0 47.1

23.3 29.9 38.1 45.0

cone angle (deg) Tolman method

221b 218b

118 145 182 212

%Vbur method

275c 227c

114 145 184 217

SUMMARY

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EXPERIMENTAL SECTION

We have conducted a preliminary exploration of the coordination chemistry of a highly functional class of 4phosphino-NHCs prepared from the abnormal reaction of a phosphaalkene and an NHC. These novel compounds are effective as bidentate bridging ligands for d-block elements, and novel complexes of gold(I) and palladium(II) have been isolated and fully characterized. Noteworthy is the binuclear complex 4a as well as those in which both the NHC and the phosphine moiety are coordinated to gold and/or palladium (6a and 5b). These complexes demonstrate the unique binding properties of 4-phosphino-NHCs that contain both a phosphine and carbene moiety and cannot form chelate complexes. We envisage future explorations of 4-phosphinoNHC ligands as bridging ligands for the development of novel coordination polymers or as precursors to novel polynuclear complexes for application in catalysis.

Table 3. Buried Volumes (%Vbur) and Tolman Cone Angles for Selected N-Heterocyclic Carbenes and Phosphines Determined Using Structural Data for Their Respective Au(I)Cl Complex %Vbura

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ref 30, 33, 34 18, 30, 33 this work this work 18, 30, 33 35 22, 30, 33 33, 36 30, 37 30, 38 30, 39 30, 40

General Considerations. Unless otherwise noted, all manipulations were performed under an atmosphere of nitrogen. Hexanes, dichloromethane, and toluene were deoxygenated with nitrogen and dried by passing through a column containing activated alumina. Tetrahydrofuran was distilled from Na/benzophenone. C6D6 was stored over molecular sieves (4 Å) before use, and ampules of CD2Cl2 were used as received from CIL. NHCs (IMes, ICy), 41,42 phosphaalkenes,43 1a,11 and (tht)AuCl44 were prepared following literature procedures. 31P, 1H, and 13C{1H} NMR spectra were recorded at room temperature on Bruker Avance 300 or 400 MHz spectrometers with chemical shifts (δ) in parts per million (ppm). Chemical shifts are referenced and reported relative to 85% H3PO4 as an external standard (δ = 0.0 for 31P) or referenced to TMS and measured relative to residual solvent peak (C6HD5 or CHDCl2: δ = 7.16 or 5.32 for 1H, respectively; C6D6 or CD2Cl2: δ = 128 or 53.8 for 13 C, respectively). Mass spectra were recorded on a Kratos MS 50 instrument in EI mode (70 eV). Elemental analyses were performed by Mr. Derek Smith in the UBC-Chemistry Microanalysis Facility. Synthesis of 2a. To a solution of (tht)AuCl (100 mg, 0.31 mmol) in THF (2 mL) was added a solution of 1a (200 mg, 0.32 mmol) in THF (2 mL). The mixture was stirred for an hour, and then an aliquot analyzed by NMR spectroscopy. The signals in the 31P (δ = −36.4 in THF) and the 13C{1H} NMR (δ = 175.2 in THF) are consistent with the formation of 2a. After removal of volatiles, the crude product was obtained as a colorless powder [yield: 175 mg (64%)], and all efforts to prepare crystals suitable for X-ray crystallography were unsuccessful. Synthesis of 3a. To a solution of (tht)AuCl (210 mg, 0.66 mmol) in THF (2 mL) was added a solution of 1a (200 mg, 0.32 mmol) in THF (2 mL). The mixture was stirred for an hour, and then the volatiles were removed in vacuo. The crude product was recrystallized from dichloromethane/ethanol. Yield: 190 mg (55%). 31 P NMR (162 MHz, CD2Cl2): δ = −0.14 (d, JHP = 16 Hz). 1H NMR (400 MHz, CD2Cl2): δ = 8.06−6.13 (m, 16H, aromatic), 6.70 (1H, vinyl), 5.57 (d, JHP = 16 Hz, 1H, CPh2H), 2.62 (br s, 3H, CH3), 2.35 (s, 3H, CH3), 2.33 (s, 3H, CH3), 2.32 (s, 3H, CH3), 2.30 (s, 3H, CH3), 2.10 (s, 3H, CH3), 2.09 (bs, 3H, CH3), 1.78 (s, 3H, CH3), 1.17 (s, 3H, CH3). 13C{1H} NMR (100 MHz, CD2Cl2): δ = 177.6, 144.6 (d, JCP = 3 Hz), 141.6, 141.1, 137.2, 137.1 (d, JCP = 4 Hz), 136.7, 135.9, 135.1, 134.9, 134.4, 132.9, 131.5, 131.4 (2C), 130.4, 130.3 (d,

a Parameters of SambVca calculations: (1) 3.50 Å was selected as the value for the sphere radius, (2) L−M bond lengths were set to 2.00 and 2.28 Å for NHCs and phosphines, respectively, (3) hydrogen atoms were omitted, and (4) scaled Bondi radii were used as recommended by Cavallo.29 bTolman’s cone angle was determined from X-ray crystallographic data following Tolman’s method where a van der Waals radius of 1.00 Å was used for hydrogen.32 cCone angle = 4.786(%Vbur) + 2.037 (R2 = 0.981).30 dStructures used to calculate % Vbur extracted from X-ray crystal structure of complex 5b. eStructures used to calculate %Vbur extracted from X-ray crystal structure of complex 3a.

Comparing 1a with other carbene ligands, its steric demand (%Vbur = 36.2) falls in the middle of the range for carbenes (% Vbur = 26.3−55.1) and, not surprisingly, is very similar to that of the parent IMes (%Vbur = 36.5). In contrast, the cyclohexylcontaining 1b (%Vbur = 32.8) displays a larger steric demand than ICy (%Vbur = 27.4). Presumably, this is a consequence of the bulky 4-phosphino moiety in 1b, which leads to a rotation of the Cy ring by 180° with respect to the other Cy moiety, leading to increased steric demand at the carbene position. The positioning of the Cy moiety in 1b also appears to ease steric demand at the phosphine moiety (%Vbur = 47.5), which is less than that in 1a (%Vbur = 57.0). The steric demand of the phosphine moiety in 1a is quite remarkable when compared to other phosphine ligands (e.g., PMes3: %Vbur = 45.0). The cone angle calculated from %Vbur is 275°,30 and the value determined from the crystallographic data for 1a following Tolman’s method is 221°.32 The large difference between these values E

DOI: 10.1021/acs.inorgchem.6b00686 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry JCP = 7 Hz), 130.1, 130.0, 129.9, 129.8, 129.7, 129.3, 129.2 (d, JCP = 3 Hz), 128.8 (d, JCP = 5 Hz), 125.0 (d, JCP = 58 Hz), 117.8 (d, JCP = 63 Hz), 50.7 (d, JCP = 36 Hz), 21.6, 21.5 (2C), 21.3, 18.5, 17.9, 16.7. MS (EI, 70 eV): 853, 852 [2, 1; M+ − AuCl], 688, 687, 686, 685, 684 [1, 3, 6, 7, 14; M+ − AuCl − CHPh2]; 168, 167 [39, 100; CHPh2+]. Anal. Calcd for C43H45N2PAu2Cl2·CH2Cl2: C, 45.15; H, 4.05; N, 2.39. Found: C, 45.85; H, 4.32; N, 2.54. Synthesis of 4a. To a solution of 1a (200 mg, 0.32 mmol) in THF (2 mL) was added a solution of (tht)AuCl (50 mg, 0.16 mmol) in THF (5 mL). The mixture was stirred for an hour, during which time a white precipitate formed. The volatiles were removed in vacuo. Crystals suitable for X-ray crystallography were obtained by recrystallization from dichloromethane/pentane in air. Yield: 170 mg (72%). 31 P NMR (162 MHz, CD2Cl2): δ = −37.8. 1H NMR (400 MHz, CD2Cl2): δ = 7.56−6.43 (m, 32H, aromatic), 6.59 (d, JHP = 2 Hz, 1H, vinyl), 5.20 (d, JHP = 5 Hz, 1H, CPh2H), 2.46 (s, 3H, CH3), 2.37 (s, 3H, CH3), 2.35 (s, 3H, CH3), 2.13 (s, 3H, CH3), 1.67 (d, JPH = 3 Hz, 3H, CH3), 1.60 (s, 3H, CH3), 1.46 (d, JHP = 3 Hz, 3H, CH3), 1.16 (d, JHP = 1 Hz, 3H, CH3), 0.71 (d, JHP = 3 Hz, 3H, CH3). 13C{1H} NMR (100 MHz, CD2Cl2): δ = 186.5, 148.3, 147.9, 144.6, 141.6 (d, JCP = 14 Hz), 141.5, 140.7 (d, JCP = 15 Hz), 140.0, 139.8, 136.5, 135.7, 135.0, 134.9, 134.4, 133.1, 132.7 (d, JCP = 24 Hz), 130.8, 129.5 (2C), 129.4, 129.3, 129.2, 128.9 (2C), 128.7, 128.2 (2C), 128.1, 127.8, 127.3, 123.1 (d, JCP = 17 Hz), 47.5 (d, JCP = 8 Hz), 23.2 (d, JCP = 35 Hz), 21.7, 21.5, 21.4, 21.2, 17.9 (d, JCP = 6 Hz), 17.5, 16.7, 16.2. Anal. Calcd for C86H90N4P2AuCl·H2O: C, 69.23; H, 6.21; N, 3.76. Found: C, 69.28; H, 6.20; N, 3.74. Synthesis of 5a. To a solution of 4a (50 mg, 0.03 mmol) in dichloromethane (1 mL) was added a solution of (tht)AuCl (25 mg, 0.08 mmol) in dichloromethane (2 mL). The mixture was stirred for an hour, and then an aliquot analyzed by NMR spectroscopy. The signals in the 31P NMR (δ = 0.6 and 0.5 in dichloromethane) are consistent with coordination of AuCl to both phosphine moieties in 4a and suggest the formation of 5a. After removal of volatiles, the crude product was obtained as a colorless powder. Yield: 55 mg (84%). Attempts to obtain single crystals suitable for X-ray crystallography were unsuccessful. Synthesis of 5b. To a solution of ICy (0.069 g, 0.30 mmol) in THF (3 mL) was added MesPC(4-C6H4F)2 (0.106 g, 0.30 mmol). The mixture was stirred overnight. An aliquot was removed, and 31P NMR spectroscopy indicated quantitative conversion of the phosphaalkene (δ = 234) to a new compound, 1b (δ = −37.6). A 1 mL aliquot of the reaction mixture was removed and added to [(tht)AuCl] (32 mg, 0.10 mmol). The mixture was stirred for 3 h, and then a second equivalent of [(tht)AuCl] (32 mg, 0.10 mmol) was added. After removal of THF solvent, the crude product was dissolved in dichloromethane, and slow diffusion of diethyl ether into the solution afforded colorless crystals suitable for X-ray crystallography. Yield: 32 mg (10%). 31 1 P{ H} NMR (121.5 MHz, CDCl3): δ = 0.17. 1H NMR (300 MHz, CDCl3): δ = 8.0 (m, 4H, aromatic), 7.8 (2H, m, vinyl), 7.5−6.9 (m, 12H, aromatic), 6.1 (2H, meta-H-Mes), 5.2 (d, JHP = 7 Hz, 2H, CAr2H), 4.6 (m, 4H, NCCyH), 2.7−0.9 (m, alkyl-H, overlap with aliphatic impurities). MS (ESI+ in MeOH) [m/z]: 1829.2 [M + H+ − AuCl2], 1071.1 [(M/2) + Na+]. Synthesis of 6a. To a solution of Pd(cod)Cl2 (157 mg, 0.55 mmol) in THF (5 mL) was added a solution of 1a (340 mg, 0.55 mmol) in THF (5 mL). The mixture was stirred for 6 h, and the volatiles were removed in vacuo to afford a yellow solid. Subsequently, this product was treated with (tht)AuCl (176 mg, 0.55 mmol) in THF (10 mL) at room temperature. After 3 h, analysis of the orange solution by 31P NMR spectroscopy revealed that the signal at −38 ppm had been replaced by a new signal at −1 ppm. An orange solid was obtained after the removal of the volatiles. The crude product was recrystallized from a concentrated CH2Cl2 solution by slow evaporation at ambient temperature. Yield: 246 mg (40%). 31 1 P{ H} NMR (121.5 MHz, C6D6): δ = −1.0 ppm. 1H NMR (300 MHz, C6D6): δ = 7.67−6.49 (m, 17H, 16 aromatic +1 vinyl), 5.17 (d, JHP = 15 Hz, 1H, CPh2H), 3.15 (s, 3H, CH3), 2.68 (s, 3H, CH3), 2.53

(s, 3H, CH3), 2.10 (s, 3H, CH3), 2.10 (s, 3H, CH3), 1.87 (s, 3H, CH3), 1.63 (s, 3H, CH3), 1.14 (s, 3H, CH3), 0.92 (s, 3H, CH3). 13 C{1H} NMR (100 MHz, C6D6): δ = 167.1 (N−C−N), 142.8 (d, JCP = 3 Hz), 140.4, 139.7, 139.0, 137.2, 137.0, 136.7, 135.8, 135.3, 134.0, 133.9, 133.6, 131.8, 130.1, 130.0 (d, JCP = 3 Hz), 129.9, 129.8 (d, JCP = 12 Hz), 129.7, 129.5, 129.4, 128.7 (d, JCP = 3 Hz), 125.4 (d, JCP = 67 Hz), 120.3, 119.4, 50.5 (d, JCP = 30 Hz), 37.5, 35.0, 29.7, 29.5, 20.7, 20.0, 19.4, 19.1. MS (ESI+ in nitromethane) [m/z]: 1119.3 [M+]. Anal. Calcd for C47H54AuCl3N2PPdS·CH2Cl2: C, 49.31; H, 4.83; N, 2.40. Found: C, 49.32; H, 4.75; N, 2.46. X-ray Crystallography. All single crystals were immersed in oil and mounted on a glass fiber. Data were collected at 90 ± 0.1 K on a Bruker X8 APEX 2 diffractomer with graphite-monochromated Mo Kα radiation. Data were collected and integrated using the Bruker SAINT45 software package and corrected for absorption effects with SADABS46 (for all others). All data sets were corrected for Lorentz and polarization effects. All structures were solved by direct methods47 and subsequent Fourier difference techniques and refined anisotropically for all non-hydrogen atoms using the SHELXTL48 crystallographic software package from Bruker-AXS. Additional crystal data and details of the data collection and structure refinement are given in Table 1. The crystals of 3a presented no crystallographic complications. The structure of 4a, 5b, and 6a each exhibited some disorder. In 4a, the oxygen of the water solvate could be refined anisotropically, but it was not possible to assign protons to specific Q-peaks. In 5b, the diethyl ether solvate was disordered over two positions (4:6), and one of the 4-fluorophenyl rings was disordered in two positions, with the major isomer (70%) being shown in Figure 3. In 6a, Pd(tht)Cl2 was disordered over two positions (9:1), with the major isomer (90%) being shown in Figure 4.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00686. 1 H and 31P NMR spectrum of 5b (PDF) Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Natural Sciences and Engineering Research Council (NSERC) of Canada for support of this work. J.I.B. thanks NSERC for PGS M and D scholarships. D.S. thanks the Deutscher Akademischer Austausch Dienst (DAAD) for financial support of an internship at UBC. We thank Dr. Eamonn Conrad for useful discussions.

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REFERENCES

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