Synthesis and Coordination Chemistry of a Tridentate o-Phenylene

Apr 9, 2009 - o-Phenylene-Bridged Diphosphine-NHC System. Tobias Steinke, Bryan K. Shaw, Howard Jong, Brian O. Patrick, and Michael D. Fryzuk*...
2 downloads 0 Views 583KB Size
Download PDF
2830

Organometallics 2009, 28, 2830–2836

Synthesis and Coordination Chemistry of a Tridentate o-Phenylene-Bridged Diphosphine-NHC System Tobias Steinke, Bryan K. Shaw, Howard Jong, Brian O. Patrick, and Michael D. Fryzuk* Department of Chemistry, UniVersity of British Columbia, 2036 Main Mall, VancouVer, British Columbia, Canada, V6T 1Z1 ReceiVed January 30, 2009

The preparation of a di-o-phenylene-bridged tridentate PCP donor set is described starting with t-BOCaniline followed by a series of steps that include lithiation, quenching with Pri2PCl, conversion to the phosphine sulfide, and assembling the unsaturated N-heterocyclic carbene unit. After desulfurization, the imidazolinium unit flanked by two phosphine units, represented as [(PCP)H]PF6 is obtained. Subsequent reaction with group 10 M(0) reagents (Ni(COD)2, Pd(PPh3)4, and Pt(PPh3)4) generates good yields of the corresponding metal hydride complexes, [(PCP)MH]PF6 salts (where M ) Ni(II), Pd(II), and Pt(II)). Each of these species has been characterized by elemental analyses, NMR spectroscopy, and X-ray crystallography. All of the structures show that the PCP unit is twisted with respect to the square plane of the d8 metal complex. Introduction While N-heterocyclic carbenes (NHCs) have a history that ¨ fele, and codates back some four decades to Wanzlick, O workers,1 most would point to the isolation of the N,NdiadamantylNHC in 1991 as a key date2,3 in the increase in interest in NHCs. Since then, they have become extremely popular as ligands in coordination chemistry and homogeneous catalysis.1,4-6 The variation possible in NHC design is immense and ranges from replacement of the nitrogen atoms in the ring to other heteroatoms, utilization of different ring sizes in the heterocycle, and of course control of steric and electronic effects by suitable choice of the heteroatom substituents.1 Another important design aspect has been the incorporation of NHC donors into polydentate arrays, usually in combination with other classical donors, such as pyridine, oxazolines, and phosphines to generate tripodal and “pincer” ligands.7-9 Recently, we described the coordination chemistry of a tridentate diamidocarbene ligand [NCN] to zirconium and tantalum precursors.10-12 This [NCN] ligand and many other * Corresponding author. E-mail: [email protected]. (1) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122– 3172. (2) Arduengo, A. J., III; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991, 113, 361–363. (3) Arduengo, A. J., III; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991, 113, 2801. (4) Bourissou, D.; Guerret, O.; Gabbaı¨, F. P.; Bertrand, G. Chem. ReV. 2000, 100, 39–91. (5) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290–1309. (6) Crabtree, R. H. J. Organomet. Chem. 2005, 690, 5451–5457. (7) Liao, C.-Y.; Chan, K.-T.; Zeng, J.-Y.; Hu, C.-H.; Tu, C.-Y.; Lee, H. M. Organometallics 2007, 26, 1692–1702. (8) Mata, J. A.; Poyatos, M.; Peris, E. Coord. Chem. ReV. 2007, 251, 841–859. (9) Pugh, D.; Danopoulos, A. A. Coord. Chem. ReV. 2007, 251, 610– 641. (10) Spencer, L. P.; Winston, S.; Fryzuk, M. D. Organometallics 2004, 23, 3372–3374. (11) Spencer, L. P.; Beddie, C.; Hall, M. B.; Fryzuk, M. D. J. Am. Chem. Soc. 2006, 128, 12531. (12) Spencer, L. P.; Fryzuk, M. D. J. Organomet. Chem. 2005, 690, 5788–5803.

functionalized “pincer” ligands such as neutral [CNC],13 monoanionic [CCC],14,15 and neutral [PCP]16 utilize spacers that consist of one or two CH2 groups between the donor substituents. In the case of the [NCN] system above, we observed deleterious C-H activation of the R-methylene unit of the ethylene linker,11 likely a result of the flexibility imparted by the ethylene backbone. In previous studies, we have developed tridentate diamidophosphine ligands with o-phenylene linkers, designated as [NPN]*, in an effort to introduce more rigidity into this latter ligand set as compared to the parent [NPN] system.17 Although we have examined some late metal chemistry with the NCN ligand and a related bidentate NC system,18 we were also interested in a neutral rigid PCP donor set that would be suitable for a variety of late transition metals. For this reason, we developed a synthesis of a PCP-array of donors using o-phenylene linkers and have initiated a study of its coordination chemistry with the group 10 elements, all of which is described herein.

Results and Discusssion Synthesis of ([PCP]H)PF6. Our initial focus was on the unsaturated NHC-based PCP system shown in Scheme 1, which we reasoned could be assembled in a manner similar to that reported for IMes;19 condensation of an appropriate aryl amine with glyoxal would produce the corresponding diimine, which (13) (a) Danopoulos, A. A.; Winston, S.; Motherwell, W. B. Chem. Commun. 2002, 1376–1377. (b) Hahn, F. E.; Jahnke, M. C.; Gomez-Benitez, V.; Morales-Morales, D.; Pape, T. Organometallics 2005, 24, 6458–6463. (14) Rubio, R. J.; Andavan, G. T. S.; Bauer, E. B.; Hollis, T. K.; Cho, J.; Tham, F. S.; Donnadieu, B. J. Organomet. Chem. 2005, 690, 5353– 5364. (15) (a) Hahn, F. E.; Jahnke, M. C.; Pape, T. Organometallics 2007, 26, 150–154. (b) Lv, K.; Cui, D. Organometallics 2008, 27, 5438–5440. (16) (a) Lee, H. M.; Zeng, J. Y.; Hu, C.-H.; Lee, M.-T. Inorg. Chem. 2004, 43, 6822–6829. (b) Hahn, F. E.; Jahnke, M. C.; Pape, T. Organometallics 2006, 25, 5927–5936. (17) MacLachlan, E. A.; Fryzuk, M. D. Organometallics 2005, 24, 1112– 1118. (18) Jong, H.; Patrick, B. O.; Fryzuk, M. D. Can. J. Chem. 2008, 86, 803–810. (19) Jafarpour, L.; Stevens, E. D.; Nolan, S. P. J. Organomet. Chem. 2000, 606, 49–54.

10.1021/om9000764 CCC: $40.75  2009 American Chemical Society Publication on Web 04/09/2009

o-Phenylene-Bridged Diphosphine-NHC System

Organometallics, Vol. 28, No. 9, 2009 2831

Scheme 1. Initial Unsaturated NHC Target via Condensation Starting from o-Diisopropylphosphinoaniline

Scheme 2. Saturated-NHC Target via Alkylation Starting from o-Diisopropylphosphinoaniline

Scheme

3.

Synthesis

of

the

Imidazolinium Diphosphine ([PCP]H)PF6 (3) o-Diisopropylphosphinoaniline (1)

could then be converted to the parent [PCP]* via condensation with formaldehyde and HCl, followed by deprotonation of the intermediate imidazolium salt. The preparation of the odiisopropylphosphinoaniline 1 (R ) Pri) follows a literature report20 and involves double lithiation of tBOC-aniline with t BuLi and quenching with ClPPri2, followed by deprotection. Unfortunately, all attempts to condense 1 (R ) iPr) with glyoxal or even 2,3-butanedione were unsuccessful, leading only to complex mixtures of products. We eventually abandoned this strategy and developed a synthesis of the saturated NHC ligand as summarized in Scheme 2. Fortunately, this also uses 1 as a key intermediate. The assembly of the saturated NHC requires alkylation chemospecifically at the aryl amine site; to ensure that the nucleophilic PPri2 group does not interfere, it was protected as the phosphine sulfide, and the resulting amine-phosphine-sulfide reacted with 1,2-dibromoethane to generate the corresponding N,N′-bis(o-diisopropylphosphinesulfide)ethylenediamine (2) in moderate yield and then further reacted with triethylorthoformate in the presence of NH4PF6 to produce the bis(phosphinesulfide) imidazolinium salt 2, which could be reduced with excess Ra-Ni in MeOH to generate bis(phosphine) imidazolinium salt 3. This is outlined in Scheme 3. Interestingly, our initial approach to the synthesis of imidazolinium 3 involved protection of the aryl phosphinoamine 1 (20) Hessler, A.; Kottsieper, K. W.; Schenk, S.; Tepper, M.; Stelzer, O. Z. Naturforsch., B 2001, 56b.

Starting

from

Phenylisocyanate

via

as the phosphine oxide and then assembly of the saturated NHC ring to generate phosphine oxide 4; however, under no conditions were we able to reduce bis(phosphineoxide) 4 to 3. A preliminary X-ray crystal structure of 4 revealed short contacts between the C-H of the NHC and the two oxygens of phosphine oxide moieties that lie above and below the imidazolinium ring; the presence of these intramolecular H-bonds likely enhances the stability of the oxide.

The imidazolinium salt ([PCP]H)PF6 (3) is soluble in THF and CH2Cl2, but insoluble in apolar solvents, such as benzene or hexanes. While 3 is stable under nitrogen atmosphere, it slowly decomposes in air. It was characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray crystallography. The 31P{1H} NMR of 3 in d8-THF shows a singlet at -6.4 ppm for the two tertiary phosphines and a septet at -143.8 ppm for the PF6- counterion. A resonance at 8.69 ppm in the 1H NMR spectrum can be assigned to the iminium

2832 Organometallics, Vol. 28, No. 9, 2009

Steinke et al. Scheme 4. Reaction of ([PCP]H)PF6 (3) with KOtBu and KN(SiMe3)2

Figure 1. Molecular structure (ORTEP) of ([PCP]H)PF6 (3). The PF6 counteranion and all hydrogen atoms (except H1) are omitted for clarity. Table 1. Selected Bond Lengths (Å) and Angles (deg) in ([PCP]H)PF6 (3) C1-N1 C1-N2 N1-C2 N2-C3

1.310(3) 1.313(3) 1.483(3) 1.481(3)

C2-C3 N1-C4 N2-C16 P1-C9

1.530(4) 1.436(3) 1.437(3) 1.847(3)

N1-C1-N2 N1-C2-C3 C1-N1-C4 C1-N1-C16

114.1(3) 102.9(2) 126.5(2) 127.5(2)

C1-N1-C2 N2-C1-N1-C3 C1-N1-C4-C9 C1-N2-C16-C21

109.8(2) -2.5(3) 47.8(4) 41.0(4)

hydrogen, which correlates to a resonance at 158 ppm in the 13 C{1H} NMR spectrum assigned to the iminium carbene carbon. Compound 3 crystallizes in the monoclinic space group C2/c. The molecular structure of 3 consists of an organic cation (see Figure 1) and the inorganic PF6 anion. The structural characteristics of this central five-membered ring are virtually identical to 1,3-dimesitylimidazolinium chloride, the precursor to the synthesis of a stable diaminocarbene.21 The short endocyclic C-N bonds (1.312(4) and 1.314(4) Å) are consistent with electron delocalization over the N-C-N fragment, which is observed in all iminium analogues. The NCN angle has a value of 114.0(3)°. The remaining bond distances N1-C2, N2-C3, and C2-C3 clearly identify these as single bonds. The imidazolinium ring is slightly puckered. The two methylene carbon centers, C2 and C3, deviate 1.6° above and 2.4° below the plane of the other three ring atoms, respectively. The o-phenylene linkers are not oriented parallel with the NHC ring; instead, the two dihedral angles defined by the atoms C1-N-Cipso-Cortho have values of 47.8° and 41.0°, respectively. Thus, the two diiisopropylphosphino moieties are located above and below the imidazolinium ring plane. As mentioned above, a preliminary solid-state structure for the bis(phosphineoxide) 4 is similar to that for 3, which accounts for the close contacts of the oxygens to the iminium C-H bond. Deprotonation of the imidazolinium salt 3 with KN(SiMe3)2 in toluene at room temperature yields the free carbene [PCP], 5, as a thermally stable but air-sensitive solid. The 1H NMR spectrum of 5 in C6D6 shows no peaks above δ 8, which is consistent with the loss of the iminium hydrogen; in addition, there are four multiplets between δ 7.58 and 7.17 that can be assigned to the four different aromatic protons of the ophenylene spacer, one singlet at δ 3.94, due to the CH2CH2 (21) Arduengo, A. J.; Goerlich, J. R.; Marshall, W. J. J. Am. Chem. Soc. 1995, 117, 11027–11028.

backbone of the NHC, one septet at δ 2.22, due to the methine protons of the isopropyl groups, and a pair of doublets of doublets at δ 1.26 and 1.14 assigned to the CH3 groups of the isopropyl moieties. A weak singlet, assigned to the carbene carbon, was apparent in the 13C{1H} NMR spectrum at δ 244.7, and the 31P{1H} NMR spectrum exhibits one singlet at δ -3.7. When imidazolinium 3 is reacted with KOtBu in THF at room temperature, the corresponding neutral “protected” carbene [PCP](H)(OtBu) 6 is formed (Scheme 2). In contrast to other examples, wherein related adducts eliminate alcohol, chloroform, or amines to unmask the carbene,22 in this particular reaction, the elimination of tBuOH under vacuum or elevated temperatures was not observed. Formation of Cationic Group 10 Metal Hydrides: ([PCP]MH)PF6. One of the most common methods to generate a metal NHC complex is the use of free carbene itself, which normally requires prior abstraction of the acidic iminium proton of the imidazolium or imidazolinium precursor with an external base (e.g., KH or KN(SiMe3)2);23,24 alternatively, these same NHC precursor salts can be added to metal complexes that already contain a basic ligand able to act as an internal base, such as in [(COD)M]2(µ-OEt)2 (M ) Rh, Ir) or in Pd(OAc)2.25 Another common way to introduce an NHC is via transmetalation using silver NHC complexes.16,26,27 In each of these processes, coordination of the NHC requires loss of HX, either prior to addition to the metal complex or during the addition. In contrast, oxidative addition of the iminium C-H bond of the NHC precursor salt is a convenient route for the introduction of the NHC, as no base is required.28-33 When equimolar quantities of the imidazolinium salt ([PCP]H)PF6 (3) were stirred with Ni(COD)2, Pd(PPh3)4, or Pt(PPh3)4 in THF at room temperature, a slight color change in the solution was observed. Concentration of the solution and cooling to (22) Trynka, T. M.; Morgan, J. P.; Sanford, M. S.; Wilhelm, T. E.; Scholl, M.; Choi, T.-L.; Sing, S.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 2546–2558. (23) Herrmann, W. A.; Elison, M.; Fischer, J.; Ko¨cher, C.; Artus, G. R. J. Chem.-Eur. J. 1996, 2, 773. (24) Jafarpour, L.; Nolan, S. P. Organometallics 2000, 19, 2055–2057. (25) Ko¨cher, C.; Herrmann, W. A. J. Organomet. Chem. 1997, 532, 261–265. (26) Lin, I. J. B.; Vasam, C. S. Coord. Chem. ReV. 2007, 251, 642– 670. (27) McGuinness, D. S.; Cavell, K. J. Organometallics 2000, 19, 741.

o-Phenylene-Bridged Diphosphine-NHC System

Organometallics, Vol. 28, No. 9, 2009 2833

Scheme 5. C-H Oxidative Addition of ([PCP]H)PF6 (3) to Ni(0), Pd(0), and Pt(0) Precursors

Figure 3. Molecular structure (ORTEP) of the cation of the palladium hydride 7b. The PF6 counterion and all hydrogen atoms except H1 are omitted for clarity. Selected bond lengths and bond angles are listed in Table 2.

-30 °C led to the isolation of the (PCP)M-hydrido complexes 7a (M ) Ni), 7b (M ) Pd), and 7c (M ) Pt) as the PF6 salts in crystalline form in 72-77% yields. The formation of the metal hydrides 7a-c was confirmed by NMR spectroscopy, single-crystal X-ray diffraction (Figures 2-4), and elemental analysis. In the 1H NMR spectrum in d8THF, the metal-hydride resonances of 7a and 7b appear at -10.73 (Ni) as a triplet (JP-H ) 53.5 Hz) and at -6.15 ppm (Pd) as a singlet, respectively; the Pt-H resonance of 7c appears as a triplet (JP-H ) 14.5 Hz) centered at -4.43 ppm with 195Pt satellites (JPt-H ) 403.2 Hz). The reason that the hydride resonance in the palladium derivative 7b is observed as a singlet is unclear. A related neutral Pd pincer complex Pd[(2,6C6H3(CH2PtBu2)2]H shows the expected triplet at -3.86 (JP-H ) 13.5 Hz).34 The 31P{1H} NMR spectra of these hydride complexes all show singlets that are shifted downfield of the free ligand to δ 47.6 (7a), 46.1 (7b), and 39.5 (7c) upon coordination; the singlet for the platinum complex 7c also displays the expected Pt satellites (JPt-P ) 1241.5 Hz). In the 13 C{1H} NMR spectra, resonances assignable to the carbenic carbons of the coordinated NHC are observed as triplets at 189.28 ppm (7a: 2JC-P ) 32 Hz), 197.28 ppm (7b: 2JC-P ) 13.5 Hz), and 196.68 (7c: 2JC-P ) 25 Hz), slightly downfield of related Pd pincer PCP complexes that have unsaturated NHC donors.16 Compounds 7a-c are noteworthy in that they are a set of completely identical group 10 metal hydride complexes that have been characterized by both solution spectroscopic and solid-

Figure 4. Molecular structure (ORTEP) of the cation of the platinum hydride 7c. The PF6 counterion and all hydrogen atoms except H1 are omitted for clarity. Selected bond lengths and bond angles are listed in Table 2. Table 2. Selected Bond Lengths (Å) and Angles (deg) for the Group 10 Hydride Complexes, ([PCP]MH)PF6 M ) Ni

M ) Pd

M ) Pt

M-C1 M-P1 M-P2 M-H1 C1-N1 C1-N2

1.8629(19) 2.1080(8) 2.1129(9) 1.38(4) 1.345(3) 1.341(3)

2.037(8) 2.266(2) 2.257(2) 1.77(7) 1.315(10) 1.341(10)

2.008(4) 2.2484(12) 2.2474(13) 1.53(5) 1.339(6) 1.341(5)

C1-M-H1 P1-M-P2 P1-M-C1 P2-M-C1

173.2(15) 169.03(2) 94.70(6) 95.90(6)

177(2) 174.90(9) 89.1(2) 89.8(2)

179(2) 178.00(4) 89.86(12) 89.32(12)

state X-ray crystallographic methods.35 A recent report described the insertion of the electron-rich, coordinately unsaturated L2M(0) complexes (M ) Ni, Pd, L ) 1,3-aryl-NHC) in the C-H bond of a imidazolium salt.31 The first Pt-hydrides derived from oxidative addition of imidazolium salts to Pt(0)-phosphine compounds were described separately.28,29,36 All three group 10 complexes 7a-c are stable both in solution and in the solid Figure 2. Molecular structure (ORTEP) of the cation of the nickel hydride 7a. The PF6 counterion and all hydrogen atoms except H1 are omitted for clarity. Selected bond lengths and bond angles are listed in Table 2.

(28) McGuinness, D. S.; Cavell, K. J.; Yates, B. F. Chem. Commun. 2001, 355–356. (29) McGuinness, D. S.; Cavell, K. J.; Yates, B. F.; Skelton, B. W.; White, A. H. J. Am. Chem. Soc. 2001, 123, 8317.

2834 Organometallics, Vol. 28, No. 9, 2009

state and can be stored under an inert atmosphere for an extended period of time. Complex 7a crystallizes in the monoclinic space group P21/ n, while for 7b the triclinic space group P1j was found and the platinum hydride 7c crystallizes in the monoclinic C2/c space group. In all three molecular structures the metal center adopts a slightly distorted square-planar geometry, but the distortion in the nickel derivative 7a is largest, as shown by the deviation from linearity of the trans donors; for example, the angle P1-Ni1-P2 in 7a is 169.03(2)°, noticeably smaller that the corresponding angles in 7b and 7c. The NHC ring is twisted in each structure, making an angle of 31.9/35.1° (7a), 35.5°/41.5° (7b), and 35.27° (7c) with the metal plane. These values are similar to those found in Pd(II) pincer complexes of [CCC],37 [CNC],38 and [PCP]16a and Pt(II) pyrazolyl complexes39 all of which have angles that range from 25.25° to 49.10°. Hence, the twisting of the NHC ring in each of 7a-c is not caused by any geometrical constraints of this particular ligand, as the observed twists match others observed with quite different ligands. Theoretical calculations for the Pd-[PCP] complexes with alkyl linkers have revealed that the rotational energy barrier about the Pd-NHC bond is rather small (ca. 4 kcal/mol).16 Similar low values can be anticipated for 7a, 7b, and7c, as a fast interconversion (atropisomerization) between two enantiomeric conformers is observed in solution. This is evident from the 1H NMR spectrum of 7a for example, which shows that the backbone ethylene unit of the NHC appears as a sharp singlet, indicating that all four protons are equivalent; if the chiral twisted conformation observed in the solid state was locked in solution (or undergoing very slow interconversion on the NMR time scale), then each methylene unit would consist of two diastereotopic protons, which would generate a more complicated AA′BB′ pattern. Similar conformational changes were observed in lutidine- and meta-xylene-based pincer compounds of the type [Pd(CDC)Br]n+ (D ) N, n ) 1; D ) C-, n ) 0)37,38 and [Pd(PCP)Cl]Cl, containing the [PCP] ligand with alkyl linkages (Vide supra). The bond distances in the coordination sphere of the complexes 7a-c exhibit no unusual features. The M1-C1 bond lengths have values of 1.8629(19) Å (7a), 2.028(4) Å (7b), and 2.005(4) Å (7c), respectively. Typically, Ni(II)-carbene distances are found in the range 1.85-1.89 Å, while the Ni(0)-carbene bonds in homoleptic Ni(IMes)2 are slightly shorter (1.827 and 1.830 Å).40,41 The Pd1-C1 bond length in (30) Gru¨ndemann, S.; Albrecht, M.; Kovacevic, A.; Faller, J. W.; Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2002, 2163–2167. (31) Clement, N. D.; Cavell, K. J.; Jones, C.; Elsevier, C. J. Angew. Chem., Int. Ed. 2004, 43, 1277–1279. (32) Bacciu, D.; Cavell, K. J.; Fallis, I. A.; Ooi, L. Angew. Chem., Int. Ed. 2005, 44, 5282–5284. (33) Viciano, M.; Mas-Marza, E.; Poyatos, M.; Sanau, M.; Crabtree, R. H.; Peris, E. Angew. Chem., Int. Ed. 2005, 44, 444–447. (34) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976, 1020–1024. (35) Fryzuk, M. D.; Clentsmith, G. K. B.; Leznoff, D. B.; Rettig, S. J.; Geib, S. J. Inorg. Chim. Acta 1997, 265, 169–177. (36) Duin, M. A.; Clement, N. D.; Cavell, K. J.; Elsevier, C. J. Chem. Commun. 2003, 400–401. (37) Tulloch, A. A. D.; Danopoulos, A. A.; Tizzard, G. J.; Coles, S. J.; Hursthouse, M. B.; Hay-Motherwell, R. S.; Motherwell, W. B. Chem. Commun. 2001, 1270–1271. (38) Gru¨ndemann, S.; Albrecht, M.; Loch, J. A.; Faller, J. W.; Crabtree, R. H. Organometallics 2001, 20, 5485. (39) Canty, A. J.; Patel, B.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2000, 599, 195–199. (40) Arduengo, A. J., III; Gamper, S. F.; Calabrese, J. C.; Davidson, F. J. Am. Chem. Soc. 1994, 116, 4391–4394. (41) Dorta, R.; Stevens, E. D.; Scott, N. M.; Costabile, C.; Cavallo, L.; Hoff, C. D.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 2485–2495.

Steinke et al.

7b of 2.028(4) Å is in the range observed for “pincer” carbenes (ca. 1.98-2.05 Å).9 A comparison of 7b with Pd-[PCP] complexes with alkyl linkers shows that the latter have slightly shorter Pd-CNHC bonds (e.g., 1.961(4) Å in [Pd(PCP)(NCMe3)](BF4)2 and 1.983(7) Å in [Pd(PCP)Cl]Cl), while these same complexes16a have Pd-P distances that are about 0.3-0.8 Å longer than in 7b. One explanation for these variations might be assigned to the different nature of the linker (sp3 vs sp2) in these systems or, more likely, due to the difference in the phosphorus donor substituents, PPh2 vs PPri2, and/or the different coligands (hydride vs chloride). Unfortunately for comparison purposes, no similar platinum tridentate pincer complexes have been reported. The Ni1-H1 bond length of 1.38(4) Å in 7a is analogous to [Ni(NHC)3(H)]BF4 (1.38(5) Å), while Pd1-H1 (1.81(5) Å) in 7b is significantly longer than the Pd-hydride distance observed in [Pd(NHC)3(H)]BF4 (1.57(3) Å).31 Interestingly, this latter compound consists of an unusual Hδ+-Hδ- (2.07 Å) interaction of the metal-hydride with one hydrogen atom of the ortho methyl groups at the mesityl-substituted NHC ligands. A weaker, but nevertheless significant Hδ+-Hδ- interaction was found in the molecular structures of 7a and 7b between the hydride and one of the hydrogen atoms of the isopropyl groups with a value of 2.170 Å (M ) Ni) and 2.184 Å (M ) Pd), respectively. The long Pd-H bond in the solid state correlates to the lack of coupling to 31P already mentioned. A related macrcocyclic PCP ligand system has been recently reported42 via an intramolecular template process on Mn(I) and Re(I) precursors. This neutral NHC system also has o-phenylene linkers between the NHC and the phosphine donors similar to our system. However, this PCP donor set is restricted to binding in a facial mode because the two phosphine ligands are also linked by an o-phenylene linker.

Conclusions In this study we have presented a new type of neutral pincer ligand of the PCP type wherein the central carbon donor is a saturated NHC. The incorporation of o-phenylene linkers is a further change included to reduce any tendency of the ligand arms to get involved in C-H activation processes previously identified in multidentate NHC systems.11 Incorporation of this tridentate ligand onto the group 10 triad of elements proceeds smoothly to generate square-planar metal hydride complexes as PF6 salts, the structures of which show considerable twisting of the ligand framework above and below the plane defined by the metal and the PCP donors. In solution, this twisting is not fixed, as the two possible chiral conformations are exchanging fast on the NMR time scale, as evidenced by the lack of diastereotopic splitting in methylene units along the backbone. Further work will focus on the coordination chemistry of this ligand set with group 9 metals and their ability to activate C-H bonds.

Experimental Section General Data. All reactions were performed by standard Schlenk techniques in an oxygen-free nitrogen atmosphere unless otherwise noted. 1H, 13C, and 31P NMR spectra were recorded on either a Bruker AV-400.13 MHz or a Bruker AV-300 instrument operating at 300.13 MHz. Chemical shifts are given relative to TMS and were referenced to the solvent resonances as internal standards. Organic (42) Kaufhold, O.; Stasch, A.; Pape, T.; Hepp, A.; Edwards, P. G.; Newman, P. D.; Hahn, F. E. J. Am. Chem. Soc. 2009, 131, 306–317.

o-Phenylene-Bridged Diphosphine-NHC System solvents were purchased anhydrous from Aldrich, sparged with nitrogen, and passed through columns containing activated alumina and molecular sieves. Deuterated solvents were purchased from Cambridge Isotope Laboratories, degassed, and dried over activated 3 Å molecular sieves prior to use. Phenyl isocyanate, tert-butanol, tert-butyllithium, chlorodiisopropylphosphine, 1,2-dibromoethane, triethyl orthoformate, and Raney-nickel (4200) were purchased from Aldrich and used without further purification. Ni(COD)2, Pd(PPh3)4, and Pt(PPh3)4 were purchased from STREM and used as received. t-BOC-aniline.20 To phenyl isocyanate (40 g, 0.3358 mol) was added neat tert-butanol (27.7 g, 0.3676 mol) at room temperature. The reaction mixture was then warmed gently to 60 °C and stirred at this temperature for 1 h and for a further 1 h at 80 °C. During this time a white solid formed. After cooling, the solid was dissolved in Et2O (about 8 g per 125 mL) and recrystallized by slow cooling to -30 °C. After filtration, the volume of the filtrate was reduced by half and a second crop collected after cooling at -30 °C. The combined crystallized fractions were dried under vacuum. Yield: 53 g (82%). 1 H NMR (CDCl3): δ 7.36 (d, JHH ) 8 Hz, CH, 2H), 7.15 (t, JHH ) 7.8 Hz, CH, 2H), 6.89 (t, JHH ) 7.2 Hz, CH, 1H), 6.15 (s br, NH, 1H), 1.51 (s, CH3, 9H). 13C{1H} NMR (CDCl3): δ 138.2, 128.9, 122.9, 118.5, 28.3. o-C6H4(NHt-BOC)(PPri2). To a solution of t-BOC-aniline (65 g, 0.334 mol) in Et2O (1 L) in a 3 L two-necked round-bottomed flask was added tert-BuLi (430 mL of a 1.7 M pentane solution, 0.735 mol) dropwise at -20 °C. After the addition, the reaction mixture was stirred at -10 °C for an additional 3 h. During this time a white precipitate formed. The reaction mixture was then cooled to -80 °C and a solution of ClPPri2 (51 g, 0.334 mol) in 150 mL of Et2O was added slowly; upon completion, the reaction mixture was warmed to ambient temperature. After stirring for 14 h a saturated solution of NaCl in 400 mL of water was added, the organic phase separated and dried over MgSO4, and the Et2O distilled to give the product as a yellow-orange residue. The product contains small amounts (8-13%) of unidentified side products as detected by 31P NMR spectroscopy (C6D6): δ -8.6, -4.4, and 92.1. For the following step, further purification was not necessary. 1 H NMR (400.13 MHz, C6D6, 298 K): δ 8.80 (m, CH, 1H), 7.26 (t, JHH ) 7 Hz, CH, 1H), 7.20 (m, CH, 1H) 6.94 (t, JHH ) 7 Hz, CH, 1H), 1.94 (sep, JHH ) 7 Hz, CH, 1H), 1.48 (s, CH3, 9H), 1.05 (dd, JHH ) 7 Hz, JHP ) 16 Hz, CH3, 6H), 0.84 (dd, JHH ) 6.85 Hz, JHP ) 12.2 Hz, CH3, 6H). 13C{1H} NMR (100.62 MHz, C6D6, 298 K): δ 153.4 (d, JP-C ) 1.5 Hz,), 145.8 (d, JP-C ) 17.7 Hz,), 133.2 (d, JP-C ) 3.1 Hz,), 131, 123.0, 119.9 (d, JP-C ) 1.5 Hz), 80.5 (s, C(CH3)3) 29.1 (s, CH3), 24.1 (d, JP-C ) 9.9 Hz), 19.4 (d, JP-C ) 7.7 Hz).31P{1H} NMR (161.98 MHz, C6D6, 298 K): δ -15.3. o-C6H4(NH2)(PPri2) (1). To a solution of o-C6H4(NHt-BOC)(PPri2) (98 g, 0.314 mol) in 500 mL of CH2Cl2 was added HCl (94 mL of 10 M solution, 0.942 mol) dropwise. Immediately, the evolution of carbon dioxide was observed, and the temperature increased to about 40 °C. Stirring was continued for 20 h at room temperature. The orange reaction mixture was slowly treated with a 10 M solution of NaOH until the pH value is about 10 and a milky aqueous phase and an orange organic layer were formed. The organic phase was separated and dried over magnesium sulfate, and the solvent removed in vacuum. The product was extracted from the residue with 500 mL of Et2O, and the solvent was removed under vacuum. Afterward the product can be extracted with 300 mL of pentane. After removal of the solvent in Vacuo, the crude product is obtained as pale yellow-orange oil. Yield: 60.3 g. Mass spectroscopy analysis of the crude product revealed the presence of two side compounds: BOC-aniline (GC-MS: m/z ) 193 [M+]) and PPri2OH (GC-MS: m/z ) 134), each in varying amounts of 13-25%. The latter byproduct gives rise to one singlet at δ 52.9 in the 31P{1H} NMR spectrum. These impurities were not separated but carried on to the next step.

Organometallics, Vol. 28, No. 9, 2009 2835 1 H NMR (C6D6): δ 7.11 (d, JHH ) 7.3 Hz, CH, 1H), 7.06 (t, JHH ) 7 Hz, CH, 1H), 6.67 (t, JHH ) 7.3 Hz, CH, 1H), 6.52 (m, CH, 1H), 4.12 (s br, NH2, 2H), 1.93 (sep, JHH ) 7 Hz, CH, 2H), 1.10 (dd, JHH ) 7 Hz, JHP ) 15.5 Hz, CH3, 6H), 0.90 (dd, JHH ) 7 Hz, JHP ) 12 Hz, CH3, 6H). 13C{1H} NMR (C6D6): δ 153.1 (JP-C ) 21.3 Hz), 133.0 (d, JP-C ) 2.9 Hz), 130.1, 117.5, 116.8 (d, JP-C ) 17.8 Hz), 115.24 (d, JP-C ) 2.9 Hz), 23.4 (d, JP-C ) 10.3 Hz), 19.0 (d, JP-C ) 8.6 Hz). 31P{1H} NMR (C6D6): δ -14.6. MS (EI): m/z (%) 209 (34) [M+], 167 (38) [M - C3H6], 124 (100) [M C6H13]. o-C6H4(NH2)(PSPri2). Elemental sulfur (3.06 g, 0.0975 mol) was slowly added to a solution of crude o-C6H4(NH2)(PPri2), 1 (20 g, 0.0957 mol), in 150 mL of toluene at room temperature. After the addition, the solution was heated to reflux for approximately 1 h, and then the solvent was removed under vacuum. The remaining orange residue was dissolved in Et2O and filtered through Celite, and the solvent was evaporated. The residue is washed with a mixture of pentane and Et2O (2:1) and dried in Vacuo. The crude product was crystallized by cooling a diethyl ether solution to -40 °C; a second crop of crystals can be obtained by adding pentane to the filtrate. Yield: 20.8 g in two batches. 1 H NMR (CDCl3): δ 7.20 (t, JHH ) 7.5 Hz, CH, 1H), 7.08 (t, JHH ) 9 Hz, CH, 1H), 6.64 (m, CH, 2H), 5.93 (s br, NH2, 2H), 2.52 (sep, JHH ) 7 Hz, CH, 2H), 1.27 (dd, JHH ) 7 Hz, JHP ) 17.7 Hz, CH3, 6H), 1.14 (dd, JHH ) 7 Hz, JHP ) 17.3 Hz, CH3, 6H). 13 C{1H} NMR (CDCl3): δ 153.6 (d, JP-C ) 4.1 Hz, CH), 132.3 (d, JP-C ) 2.4 Hz, CH), 130.8 (d, JP-C ) 7.5 Hz, CH), 118.1 (d, JP-C ) 7.5 Hz, CH), 116.1 (d, JP-C ) 10.4 Hz, CH), 105.1 (d, JP-C ) 70.1 Hz, CH), 28.6 (d, JP-C ) 50.5 Hz, CH), 16.5 (d, JP-C ) 2.4 Hz, CH3), 15.9. 31P{1H} NMR (CDCl3): δ 62.8. Anal. Calcd for C12H20NPS: C 59.72; H 8.35; N 5.80. Found: C 60.03; H 8.63; N 6.10. o-C6H4(PSPri2)(NHCH2CH2NH)(PSPri2)o-C6H4 (2). Following a similar literature procedure,43 o-C6H4(NH2)(PSPri2) (11 g, 0.0456 mol) was heated to 110 °C to generate a melt, and to it was added neat 1,2-dibromoethane (2.14 g, 0.0114 mol) dropwise with stirring while the temperature was maintained at 110 °C. The mixture was further stirred for 2 h at 130 °C and then cooled to 80 °C, and aqueous KOH (6.2 M, 5 mL) was added while the stirring was maintained. Upon cooling to room temperature, the mixture was extracted with CH2Cl2, dried over MgSO4, and filtered, and the solvent was removed under vacuum. The residue was extracted with 100 mL of Et2O, and the solid residue dried under vacuum. The pale yellow Et2O extract was concentrated under reduced pressure and cooled to -40 °C, giving 4.34 g of starting o-C6H4(NH2)(PSPri2) as pale yellow crystals, which can subsequently be recycled. The colorless product can be recrystallized by cooling a concentrated THF solution to -30 °C. Yield: 2.21 g (38.2%). 1 H NMR (CDCl3): δ 8.26 (s, br, NH, 1H), 7.30 (t, JHH ) 7.75 Hz, CH, 1H), 7.09 (m, CH, 1H), 6.76 (m, CH, 1H), 6.64 (m, CH, 1H), 3.43 (s, CH2, 4H), 2.51 (sep, JHH ) 7 Hz, CH, 4H), 1.25 (dd, JHH ) 7 Hz, JHP ) 17.7 Hz, CH3, 12H), 1.14 (dd, JHH ) 7 Hz, JHP ) 17.3 Hz, CH3, 12H). 13C{1H} NMR (C6D6): δ 155.1 (d, JP-C ) 3.8 Hz, CH), 133.9 (d, JP-C ) 2.3 Hz, CH), 132.3 (d, JP-C ) 6.9 Hz, CH), 115.9 (d, JP-C ) 10.7 Hz), 113.1 (d, JP-C ) 6.9 Hz, CH), 105.5 (d, JP-C ) 70.5 Hz), 43.7, 29.6 (d, JP-C ) 50.6 Hz, CH), 17.5 (d, JP-C ) 2.3 Hz, CH3), 16.8 (s, CH3). 31P{1H} NMR (CDCl3): δ 62.0. Anal. Calcd for C26H42N2P2S2: C 61.39; H 8.32; N 5.50. Found: C 61.62; H 8.30; N 5.88. [o-C6H4(PSPri2)(NC3H5N)(PSPri2)o-C6H4]PF6. Following a literature procedure,44 an intimate mixture of 2 (2.12 g, 4.173 mmol), NH4PF6 (0.680 g, 4.173 mmol), and triethyl orthoformate (8 mL) was heated to 120 °C for 3 h with stirring. The ethanol formed

(43) Mimoun, H.; de Saint Laumer, Y.; Giannini, L.; Scopelliti, R.; Floriani, C. J. Am. Chem. Soc. 1999, 121, 6158–6166. (44) Saba, S.; Brescia, A.; Kaloustian, M. K. Tetrahedron Lett. 1991, 32, 5031–5034.

2836 Organometallics, Vol. 28, No. 9, 2009 during the reaction and excess triethyl orthoformate were removed under vacuum. The crude product was washed with toluene, extracted with CH2Cl2, and filtered. After removal of the solvent, the product was washed with Et2O. The colorless product can be recrystallized in a mixture of CH2Cl2 and Et2O. Yield: 2.41 g (87.0%). 1H NMR (CDCl3): δ 7.72 (m, CH, 9H), 4.60 (s, CH2, 4H), 2.63 (sep, JHH ) 6.8 Hz, CH, 4H), 1.27 (dd, JHH ) 6.7 Hz, JHP ) 18.4 Hz, CH3, 12H), 1.07 (dd, JHH ) 6.9 Hz, JHP ) 18 Hz, CH3, 12H). 13C{1H} NMR (C6D6): δ 158.5 (s, CH), 140.2, 134.2, 132.9, 131.2 (d, JP-C ) 1.1 Hz), 125.8, (d, JP-C ) 60.9 Hz), 55.3 (s, CH3), 30.9 (d, JP-C ) 50.6 Hz, CH), 16.9 (d, JP-C ) 3.4 Hz, CH3), 16.0 (s, CH3). 31P{1H} NMR (CDCl3): δ 66.6, -143.8 (sep). Anal. Calcd for C27H41F6N2P3S2: C 48.79; H 6.22; N 4.21. Found: C 48.53; H 6.33; N 4.27. ([PCP]H)PF6 (3). Desulfurization was carried out following a literature procedure.45 A mixture of [o-C6H4(PSPri2)(NC3H5N)(PSPri2)o-C6H4]PF6 (2.3 g, 3.464 mmol) and Raney-nickel (20 g, 340.773 mmol) in methanol (70 mL) was stirred at room temperature for 24 h, during which time periodic monitoring by 31P NMR indicated that desulfurization was complete. The excess Raneynickel and nickel sulfide were removed by filtration through Celite, and the solvent was removed under vacuum. The remaining residue was then dissolved in CH2Cl2 and filtered through Celite. Following removal of solvent the product was washed with Et2O and dried under vacuum. The product was crystallized from a mixture of CH2Cl2, Et2O, and hexanes. Yield: 1.46 g (70.2%). 1H NMR (400.13 MHz, d8-THF, 298 K): δ 8.69 (s, CH, 1H), 7.88 (m, CH, 2H), 7.74 (d, JHH ) 7.6 Hz, CH, 2H), 7.57 (t, JHH ) 7.6 Hz, CH, 2H), 7.52 (t, JHH ) 7.4 Hz, CH, 2H) 4.69 (s, CH2, 4H), 2.27 (sep, JHH ) 7 Hz, CH, 4H), 1.22 (dd, JHH ) 7 Hz, JHP ) 15.3 Hz, CH3, 12H), 0.95 (dd, JHH ) 7 Hz, JHP ) 12.2 Hz, CH3, 12H). 13C{1H} NMR (100.62 MHz, d8-THF, 298 K): δ 158.0 (s, CH), 144.1 (d, JP-C ) 23.4 Hz), 135.3, 134.6 (d, JP-C ) 30.1 Hz), 132.6, 130.7, 128.8, 55.6 (d, JP-C ) 11.1, CH2), 21.2 (d, JP-C ) 20.5 Hz, CH), 20.4 (d, JP-C ) 10.7 Hz, CH3) 31P{1H} NMR (161.9 MHz, d8THF, 298 K): δ -6.4, -143.8 (sep). Anal. Calcd for C27H41F6N2P3: C 54.00; H 6.88; N 4.66. Found: C 54.16; H 7.01; N 4.87. [PCP] (5). To a mixture of solid ([PCP]H)PF6, 3 (100 mg, 0.167 mmol), and KN(SiMe3)2 (46.6 mg, 0.234 mmol) was added toluene (5 mL). After stirring for 1 h the solution was filtered through Celite and the solvent was removed. 1H NMR (C6D6, 300.13 MHz, 298 K): δ 7.56 (m, 2H, CH), 7.49 (m, 2H, CH), 7.32 (t, JHH ) 7.5 Hz, 2H, CH), 7.17 (t, JHH ) 7.5 Hz, 2H, CH), 3.94 (s, 4H, CH2), 2.22 (sep, JHH ) 7 Hz, 2H, CH2), 1.26 (dd, JHH ) 7 Hz, JHP ) 13.1 Hz, 12H, CH3), 1.14 (dd, JHH ) 7 Hz, JHP ) 12.9 Hz, 12H, CH3). 13 C{1H}NMR (d8-THF, 100.6 MHz, 298 K): δ 244.7, 150.2 (d, JP-C ) 20.7 Hz, CH), 133.1 (d, JP-C ) 3.3 Hz, CH), 129.1, 125.3 d, JP-C ) 3.5 Hz, CH), 125.0, 52.8, 24.4 (d, JP-C ) 14.8 Hz, CH), 20.0 (d, JP-C ) 13.8 Hz, CH3). 31P{1H} NMR (d8-THF, 121.5 MHz, 298 K): δ -3.7. [PCP](H)(OtBu) (6). A J. Young NMR tube was charged with 100 mg (0.167 mmol) of ([PCP]H)PF6 and 18.7 mg (0.167 mmol) of KOtBu in 1 mL of d8-THF. 1H, 13C, and 31P NMR were recorded after 2 h at room temperature. 1H NMR (d8-THF, 400.13 MHz, 298 K): δ 7.68 (m, 2H, CH), 7.37 (d, JHH ) 7.6 Hz, 2H, CH), 7.29 (t, JHH ) 7.4 Hz, 2H, CH), 7.07 (t, JHH ) 7.3 Hz, 2H, CH), 6.62 (s, 1H, CH), 4.12 (t, JHH ) 6.6 Hz, 2H, CH2), 3.09 (t, JHH ) 6.6 Hz, 2H, CH2), 2.21 (sep, JHH ) 7 Hz, 2H, CH2), 2.07 (sep, JHH ) 7 Hz, 2H, CH2), 1.26 (dd, JHH ) 6.8 Hz, JHP ) 13.7 Hz, 6H, CH3), 1.13 (s, 9H, OtBu), 1.10 (dd, JHH ) 7.3 Hz, JHP ) 12.3 Hz, 6H, CH3), 1.04 (dd, JHH ) 7.1 Hz, JHP ) 13.6 Hz, 6H, CH3), 0.98 (dd, JHH ) 7.2 Hz, JHP ) 10.7 Hz, 6H, CH3). 13C{1H}NMR (d8-THF, 100.6 MHz, 298 K): δ 150.9 (d, JP-C ) 21.3 Hz, CH), 130.0 (CH), 126.8 (CH), 122.8 (d, CH, JP-C ) (45) Gilbertson, S. R.; Wang, X. J. Org. Chem. 1996, 61, 434–435.

Steinke et al. 6 Hz), 121.3 (CH), 94.6 (CN2), 69.6 (OCMe3), 49.1 (CH2), 29.7 (CH3 on OtBu), 23.5 (d, JP-C ) 18.0 Hz), 20.1 (d, JP-C ) 13.8 Hz), 18.4 (d, JP-C ) 16.9 Hz), 17.8 (d, JP-C ) 14.2 Hz), 17.5 (d, JP-C ) 15.2 Hz), 17.2 (d, JP-C ) 13.5 Hz). 31P{1H} NMR (d8-THF, 161.9 MHz, 298 K): δ -1.9, 143.8 (sep). ([PCP]NiH)PF6 (7a). A mixture of ([PCP]H)PF6, 3 (545 mg, 0.908 mmol), and Ni(COD)2 (250 mg, 0.908 mmol) in THF (10 mL) was left to stir for 36 h at room temperature. During this time the pale yellow reaction mixture changed to yellow-brown and a precipitate is formed. The solution was then concentrated and cooled at -30 °C to generate a yellow solid. Yield: 438 mg (73.2%). X-ray quality crystals were grown by slowly cooling a concentrated THF solution to -30 °C. 1H NMR (d8-THF, 300.13 MHz, 298 K): δ 7.65 (m, 4H, CH), δ 7.53 (m, 2H, CH), 7.32 (t, JHH ) 7.3 Hz, 2H, CH), 4.41 (s, 4H, CH2), 2.62 (s, br, 4H, CH), 1.15 (dd, JHH ) 7.4 Hz, JHP ) 16.1 Hz, 12H, CH3), 1.07 (dd, JHH ) 7.2 Hz, JHP ) 15.3 Hz, 12H, CH3), -10.72 (t, 2JPH ) 53.5 Hz, NiH). 13C{1H} NMR (CD2Cl2, 100.6 MHz, 298 K): δ 189.28 (t, 2JCP ) 32 Hz), 144.51 (t, 2JCP ) 4.6 Hz), 133.56 (s), 131.93 (s), 127.16 (s), 121.21 (t, 2 JCP ) 2.3 Hz), 117.48 (t, JCP ) 16 Hz), 52.54 (s), 19.51 (s), 18.48 (s). 31P{1H} NMR (d8-THF, 121.5 MHz, 298 K): δ 47.6, -143.8 (sep). Anal. Calcd C27H41N2F6P3Ni: C 49.19; H 6.27; N 4.25. Found: C 49.28; H 6.30; N 4.14. ([PCP]PdH)PF6 (7b). The procedure for 7b is similar to the synthesis of 7a, although the consumption of the starting materials ([PCP]H)PF6 (3) (311 mg, 0.518 mmol) and Pd(PPh3)4 (600 mg, 0.908 mmol) in THF (10 mL) was complete after 30 min, as monitored by 31 P NMR spectroscopy. 7b was obtained as a light yellow crystalline product, after cooling the concentrated THF solution to -30 °C and washing several times with Et2O. Yield: 284 mg (77.6%). 1H NMR (d8-THF, 300.13 MHz, 298 K): δ 7.64 (m, 6H, CH), 7.35 (t, JHH ) 7.2 Hz, 2H, CH), 4.50 (s, 4H, CH2), 2.63 (s br, 4H, CH), 1.17 (dd, JHH ) 8 Hz, JHP ) 16.1 Hz, 12H, CH3), 1.07 (dd, JHH ) 8 Hz, JHP ) 16.1 Hz, 12H, CH3), -6.1 (s, 1H, NiH. 31P{1H} NMR (d8-THF, 121.5 MHz, 298 K): δ 46.1, 143.8 sep. 13C{1H} NMR (CD2Cl2, 100.6 MHz, 298 K): δ 197.28 (t, 2JCP ) 13.5 Hz), 146.88 (t, 2JCP ) 5 Hz), 133.48 (s), 133.03 (s) 128.42 (s), 121.71 (s), 116.28 (t, JCP ) 16 Hz), 51.48 (s), 23.99 (t, JCP ) 14 Hz), 18.70 (t, 2JCP ) 3 Hz), 18.34 (s). Anal. Calcd for C27H41N2F6P3Pd: C 45.90; H 5.84; N 3.96. Found: C 46.36; H 5.36; N 3.72. ([PCP]PtH)PF6 (7c). The procedure for 7c is the same as for 7a starting with ([PCP]H)PF6, 3 (100 mg, 0.166 mmol), and Pt(PPh3)4 (207 mg, 0.166 mmol) in THF (8 mL). Yield: 96 mg (72.4%). 1H NMR (d8-THF, 300.13 MHz, 298 K): δ 7.58 (m, 6H, CH), 7.37 (m, 2H, CH), 4.45 (s, 4H, CH2), 2.65 (s br, 4H, CH), 1.17-1.04 (m, 24 H, CH3), -4.43 (t with Pt satellites, JP-H ) 14.5 Hz, JPt-H ) 403.2 Hz, 1H, PtH). 13C NMR (d8-THF, 100.6 MHz, 298 K): δ 196.68 (t, 2JCP ) 25 Hz), 148.42 (t, 2JCP ) 15 Hz), 133.90 (s), 133.76 (s), 126.07 (s), 122.49 (s), 115.88 (t, JCP ) 20 Hz) 51.97 (s), 24.58 (t, JCP ) 18 Hz), 18.63 (s), 18.52 (s). 31P{1H} NMR (d8-THF, 121.5 MHz, 298 K): δ 39.5 (s with Pt satellites JPt-P ) 1241.5 Hz), -143.8 (sep). Anal. Calcd for C27H41N2F6P3Pt: C 40.76; H 5.15; N 3.52. Found: C 41.11; H 5.00; N 3.43.

Acknowledgment. Generous financial support was provided by the Petroleum Research Fund, administered by the American Chemical Society. We also thank the Alexander von Humboldt Stiftung for a Feodor Lynen Fellowship for T.S. Supporting Information Available: Crystallographic data for 3, 7a, 7b, and 7c (CIF files); experimental details for X-ray structure determinations. This information is available free of charge via the Internet at http://pubs.acs.org. OM9000764