Insertion Reactions and Catalytic Hydrophosphination by

Apr 30, 2010 - ‡Department of Chemistry, Vassar College, Poughkeepsie, New York 12604. Received March 19, 2010. Triamidoamine-supported zirconium ...
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Organometallics 2010, 29, 2557–2565 DOI: 10.1021/om100216f

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Insertion Reactions and Catalytic Hydrophosphination by Triamidoamine-Supported Zirconium Complexes Andrew J. Roering,† Sarah E. Leshinski,† Stephanie M. Chan,† Tamila Shalumova,‡ Samantha N. MacMillan,‡ Joseph M. Tanski,‡ and Rory Waterman*,† †

Department of Chemistry, University of Vermont, Burlington, Vermont 05405, and ‡ Department of Chemistry, Vassar College, Poughkeepsie, New York 12604 Received March 19, 2010

Triamidoamine-supported zirconium phosphido complexes, (N3N)ZrPRR0 (N3N=N(CH2CH2NSiMe3)33-; R = alkyl, aryl; R0 = R, H), have been shown to catalyze the hydrophosphination of terminal alkynes as well as that of symmetric aryl and alkyl carbodiimides. A mechanism based on insertion of the substrate into the Zr-P bond is proposed on the basis of competition experiments and model examples of stoichiometric insertion reactions of polar, small-molecule substrates possessing CdO, CdN, CtN, and CdS functionalities into the Zr-P bond. Molecular structures of the insertion products (N3N)ZrNdC(PHCy)Ph (4), (N3N)ZrNdC(PPh2)Ph (5), and (N3N)ZrPhNC(O)PPh2 (11), as well as (N3N)Zr[η2(N,N)-(iPrN)2C(PPh2)] (9), a key intermediate in the catalytic hydrophosphination of carbodiimides, have been determined.

Introduction The synthesis of carbon-phosphorus σ bonds is an attractive transformation for chemical applications, including the preparation of biologically active molecules, transitionmetal ligands, and polymers.1 A wide variety of preparative routes are possible for the synthesis of P-C bonds. Heterofunctionalization of unsaturated organic molecules is an appealing method, given the high atom economy and efficiency of this type of reaction. Catalytic heterofunctionalization reactions that form P-C bonds, including hydrophosphination,2 hydrophosphinylation,3 and hydrophosphorylation,4 have been the subject of multiple reviews. Hydrophosphination has been well studied using latetransition-metal, lanthanide, and group 2 catalysts. However, early-transition-metal catalysts have seen far less attention in the literature. A common mechanistic theme of many late-metal hydrophosphination catalysts is insertion of the unsaturated substrate into a metal-phosphorus bond. For example, late-metal catalysts undergo a series of elementary steps, including the oxidative addition of P-H bonds, insertion

of substrate into the metal-phosphorus bond, and reductive elimination to facilitate hydrophosphination of organic molecules.2b,c A noteworthy exception is the nickel-based catalyst reported by Togni, which appears to proceed via 1,4addition of phosphine to a coordinated substrate.5 Substrate insertion into metal-phosphorus bonds is proposed in the intramolecular hydrophosphination effected by lanthanide catalysts.6 Group 2 catalysts reported by Barrett and Hill involve insertion of unsaturated organic molecules, including aryl alkenes and alkynes7 as well as carbodiimides,8 into the metal-phosphorus bond. Interestingly, the only reported early-transition-metal hydrophosphination catalyst, discovered by Mindiola and co-workers,9 does not appear to proceed via insertion into the metal-phosphorus bond; rather, a terminal titanium-phosphinidene complex undergoes a [2 þ 2] cycloaddition with an alkyne in a direct analogy to early-transition-metal hydroamination catalysts.10 Similar [2 þ 2] cycloaddition reactions between polar unsaturated molecules and zirconium-phosphinidene complexes to produce phosphametallacycles have been reported by Stephan and co-workers.11 Moreover, these [2 þ 2] cycloaddition reactions appear to be commonplace for phosphinidene

*To whom correspondence should be addressed. E-mail: rory.waterman@ uvm.edu. (1) (a) Herbert, D. E.; Mayer, U. F. J.; Manners, I. Angew. Chem., Int. Ed. 2007, 46 (27), 5060–5081. (b) Clark, T. J.; Lee, K.; Manners, I. Chem. Eur. J. 2006, 12 (34), 8634–8648. (c) Waterman, R. Curr. Org. Chem. 2008, 12, 1322–1339. (d) Masuda, J. D.; Hoskin, A. J.; Graham, T. W.; Beddie, C.; Fermin, M. C.; Etkin, N.; Stephan, D. W. Chem. Eur. J. 2006, 12 (34), 8696–8707. (e) Gauvin, F.; Harrod, J. F.; Woo, H. G. Adv. Organomet. Chem. 1998, 42, 363–405. (f) Waterman, R. Dalton Trans. 2009, No. 1, 18–26. (2) (a) Glueck, D. S. Chem. Eur. J. 2008, 14 (24), 7108–7117. (b) Glueck, D. S. Dalton Trans. 2008, No. 39, 5276–5286. (c) Glueck, D. S. Coord. Chem. Rev. 2008, 252 (21-22), 2171–2179. (3) (a) Coudray, L.; Montchamp, J.-L. Eur. J. Org. Chem. 2008, 2008 (21), 3601–3613. (b) Montchamp, J.-L. J. Organomet. Chem. 2005, 690 (10), 2388–2406. (4) Baillie, C.; Jianling Xiao, C. Curr. Org. Chem. 2003, 7 (5), 477.

(5) (a) Sadow, A. D.; Haller, I.; Fadini, L.; Togni, A. J. Am. Chem. Soc. 2004, 126 (45), 14704–14705. (b) Sadow, A. D.; Togni, A. J. Am. Chem. Soc. 2005, 127 (48), 17012–17024. (6) Motta, A.; Fragala, I. L.; Marks, T. J. Organometallics 2005, 24 (21), 4995–5003. (7) Crimmin, M. R.; Barrett, A. G. M.; Hill, M. S.; Hitchcock, P. B.; Procopiou, P. A. Organometallics 2007, 26 (12), 2953–2956. (8) Crimmin, M. R.; Barrett, A. G. M.; Hill, M. S.; Hitchcock, P. B.; Procopiou, P. A. Organometallics 2008, 27 (4), 497–499. (9) Zhao, G.; Basuli, F.; Kilgore, U. J.; Fan, H.; Aneetha, H.; Huffman, J. C.; Wu, G.; Mindiola, D. J. J. Am. Chem. Soc. 2006, 128 (41), 13575–13585. (10) (a) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1988, 110 (26), 8729–8731. (b) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J. Am. Chem. Soc. 1992, 114 (5), 1708–1719.

r 2010 American Chemical Society

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complexes of various metals.1f For example, Hillhouse and co-workers have shown that reactions of alkenes and alkynes with nickel phosphinidene produce phosphiranes and phosphirenes through a [2 þ 2] cycloaddition.12 Despite the observed cycloaddition chemistry, there is ample precedent for insertion reactivity among early-metal phosphido derivatives since the first such example, a 1,2insertion of carbon monoxide into the M-P bond of Cp*HfCl2(PtBu2), elucidated by Roddick and Bercaw.13 Since then, the insertion chemistry of terminal group 4 metal-phosphido complexes supported by cyclopentadienyl ligands has been explored by the groups of Hey-Hawkins14 and Stephan.15 The ease with which (N3N)Zr-PRR0 derivatives are prepared as part of their application for P-P16 and P-E17 bond-forming catalysis and the unlikely generation of (N3N)Zr-phosphinidene complexes suggested that insertion-based hydrophosphination may be a facile reaction for this system.1c,18 We have explored this chemistry and herein report the insertion reactivity of primary and secondary zirconium phosphido complexes of the form (N3N)ZrPRR0 (N3N=N(CH2CH2NSiMe3)33-; R=Ph, Cy; R0 =Ph, H) as well as the catalytic hydrophosphination of both terminal alkynes and carbodiimides by (N3N)ZrPPh2 (3).

Results and Discussion Insertion Chemistry. The preamble to catalytic hydrophosphination by triamidoamine-supported zirconium complexes was an investigation of stoichiometric insertion reactions of unsaturated, polar small molecules into the Zr-P bond of the terminal phosphido complexes (N3N)ZrPHCy (1), (N3N)ZrPHPh (2), and (N3N)ZrPPh2 (3).16,19 These reactions appear to be general, in that a variety of substrates featuring unsaturated C-N, C-O, and C-S bonds have been shown to insert into Zr-P bonds. CtN Bonds. Reaction of 1 with benzonitrile afforded the 1,2-insertion product (N3N)ZrNdC(PHCy)Ph (4) as analytically pure, pink microcrystals in 86% yield (eq 1). Though the 31P{1H} NMR spectrum resonance displays the expected singlet at δ 4.1, the 1H NMR spectrum reveals several more diagnostic features. The first feature is the P-H proton appearing as a doublet of doublets at δ 4.47 (JPH =224 Hz, JHH=7 Hz). The second feature of the 1H NMR spectrum is the unusual splitting of the methylene groups of the triamidoamine ligand. Whereas other (N3N)ZrX complexes display pseudo-C3v symmetry, as evidenced by the apparent (11) Hou, Z.; Breen, T. L.; Stephan, D. W. Organometallics 1993, 12 (8), 3158–3167. (12) (a) Waterman, R.; Hillhouse, G. L. J. Am. Chem. Soc. 2003, 125 (44), 13350–13351. (b) Waterman, R.; Hillhouse, G. L. Organometallics 2003, 22 (25), 5182–5184. (c) Aktas, H.; Slootweg, C. J.; Lammertsma, K. Angew. Chem., Int. Ed. 2010, 49, 2–14. (13) Roddick, D. M.; Santarsiero, B. D.; Bercaw, J. E. J. Am. Chem. Soc. 1985, 107 (16), 4670–4678. (14) (a) Lindenberg, F.; Sieler, J.; Hey-Hawkins, E. Polyhedron 1996, 15 (9), 1459–1464. (b) Hey, E.; Lappert, M. F.; Atwood, J. L.; Bott, S. G. Polyhedron 1988, 7 (19-20), 2083–2086. (15) Stephan, D. W. Angew. Chem., Int. Ed. 2000, 39 (2), 314–329. (16) Waterman, R. Organometallics 2007, 26 (10), 2492–2494. (17) Roering, A. J.; MacMillan, S. N.; Tanski, J. M.; Waterman, R. Inorg. Chem. 2007, 46 (17), 6855–6857. (18) Ghebreab, M. B.; Shalumova, T.; Tanski, J. M.; Waterman, R. Polyhedron 2010, 29 (1), 42–45. (19) Roering, A. J.; Maddox, A. F.; Elrod, L. T.; Chan, S. M.; Ghebreab, M. B.; Donovan, K. L.; Davidson, J. J.; Hughes, R. P.; Shalumova, T.; MacMillan, S. N.; Tanski, J. M.; Waterman, R. Organometallics 2009, 28 (2), 573–581.

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Figure 1. Molecular structure of 4 with thermal ellipsoids drawn at the 35% level. Hydrogen atoms, except for H(1), are omitted for clarity. Table 1. Selected Bond Lengths (A˚) and Angles (deg) for Complex 4 Zr-N(5) N(5)-C(16) C(16)-P C(23)-P

2.059(1) 1.262(2) 1.870(1) 1.859(1)

Zr-N(2) Zr-N(1) Zr-N(3) Zr-N(4)

2.084(1) 2.086(1) 2.096(1) 2.504(1)

Zr-N(5)-C(16) N(5)-C(16)-P C(23)-P-C(16)

175.3(1) 119.1(1) 107.5 (1)

N(5)-Zr-N(2) N(5)-Zr-N(1) N(5)-Zr-N(3) N(5)-Zr-N(4)

105.16(4) 104.38(4) 108.12(4) 177.81(4)

equivalence of the three methylene groups each R and β to the pseudo-apical amine nitrogen, complex 4 has lost this feature. Two sets of complex multiplets, resonating at δ 2.45 and 3.35, suggest diasterotopic methylene substituents of similar chemical shift for the ethylene backbone. The diagnostic vibrations νPH 2308 cm-1 and νCN 1610 cm-1 were observed in the infrared spectrum of 4 as well. X-ray-quality single crystals of 4 were grown from concentrated ethereal solutions kept at -30 °C for extended periods. The molecular structure of 4, shown in Figure 1, confirms the structural assignment from spectroscopic data. Complex 4 displays trigonal-bipyramidal-like geometry with a weak axial amine interaction: Zr-Naxial = 2.504(1) A˚ (Table 1). The imine carbon-nitrogen bond length (CdN = 1.262(2) A˚) falls within the range of other C-N bond lengths for zirconium iminato complexes, while the metal-nitrogen bond length of 4, Zr-N(5) = 2.059 A˚, is slightly longer than in previously reported iminato ligands.11,20

Reaction of 3 with benzonitrile afforded analytically pure, orange crystals of (N3N)ZrNdC(PPh2)Ph (5) in 72% yield (20) Segerer, U.; Blaurock, S.; Sieler, J.; Hey-Hawkins, E. Organometallics 1999, 18 (15), 2838–2842.

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Table 2. Selected Bond Lengths (A˚) and Angles (deg) for Complex 5

Figure 2. Molecular structure of 5 with thermal ellipsoids drawn at the 35% level. Hydrogen atoms are omitted for clarity.

(eq 2). The 1H NMR spectrum of 5 reveals pseudo-C3v symmetry with respect to the triamidoamine ligand. The 13 C NMR spectrum of 5 is highlighted by the imine carbon resonance at δ 144, which occurs as a doublet with JPC = 39 Hz. This is similar to that of 4, which can be seen in the 13C NMR spectrum as a doublet at δ 187 (JPC = 28 Hz). Additional support for the structure of 5 comes from the infrared spectrum with νCN 1630 cm-1. Confirmation of the structure derived from spectroscopic data came from an X-ray diffraction study. Single crystals of 5 suitable for diffraction were prepared by cooling concentrated ethereal solutions kept at -30 °C for extended periods. The solidstate structure of 5, shown in Figure 2, reveals a trigonal bipyramidal like structure with a weak axial amine interaction (Zr-Naxial = 2.462(1) A˚) with Zr-N(1) = 2.059(1) A˚ and CdN = 1.257 A˚ (Table 2). Complex 5 is isostructural with 4 and is highly related to other zirconium iminato complexes.11,20

Insertion chemistry can be thwarted by more reactive functionalities. Treatment of 3 with benzophenone imine resulted in a ligand exchange reaction, yielding the known iminato compound (N3N)ZrNdCPh2 as dark orange crystals in 64% yield with concomitant formation of Ph2PH, presumably due to the relatively strong Zr-N bond formed in the ligand exchange reaction.19 CdO Bonds. Primary phosphido complexes undergo 1,2insertion reactions with ketones (eq 3). Reaction of 2 with acetone resulted in the formation of (N3N)ZrOC(CH3)2PHPh (6) as an analytically pure, colorless powder in 95% yield. Unlike other insertions that utilize 3 as a starting material, reaction of acetone with complex 2 to form 6 results in the formation of a chiral phosphorus atom. Two alkoxide methyl resonances were well resolved as doublets at δ 1.71 (JHH=38 Hz) and δ 1.70 (JHH=49 Hz) for the enantiomers of 6 in the 1H NMR spectrum. Both methylene groups R and β to the apical amine nitrogen of the ligand backbone are

Zr-N(5) N(5)-C(16) C(16)-P C(29)-P C(23)-P

2.053(1) 1.257(2) 1.887(2) 1.824(2) 1.827(2)

Zr-N(1) Zr-N(2) Zr-N(3) Zr-N(4)

2.092(1) 2.124(1) 2.091(1) 2.462(1)

Zr-N(5)-C(16) C(29)-P-C(23) C(29)-P-C(16) C(23)-P-C(16)

172.6(1) 103.13(7) 102.40(7) 101.61(7)

N(5)-Zr-N(1) N(5)-Zr-N(2) N(5)-Zr-N(3) N(5)-Zr-N(4)

109.33(5) 105.69(5) 102.50(3) 173.12(5)

seen at δ 2.35 and 3.24 as overlapping multiplets due to each enantiomer of complex 6. To our best approximation, these resonances appear as overlapping AA0 A00 BB0 B00 spin systems. However, efforts to accurately simulate the 1H NMR spectra have thus far failed. The primary phosphido hydrogen is clearly visible as a doublet at δ 4.61 (JPH =203 Hz) in the 1H NMR spectrum. The 13C NMR spectrum is highlighted by the quaternary carbon as a doublet at δ 30.8 (JPC= 29 Hz). Interestingly, the methyl groups of the acetone insertion can be seen at very different peaks in the 13C NMR spectrum at δ 80.1 and 34.2. Presumably this inequivalence is due to the chiral phosphine. The P-H bond can be seen as a weak signal in the infrared at νPH 2302 cm-1. The 31 P NMR spectrum was largely unremarkable but is consistent with the formula given.

Heterocumulenes. The CdN bonds of carbodiimides readily insert into the Zr-P bond. Complex 3 was treated with N,N0 -dicyclohexyl-, N,N0 -diphenyl-, and N,N0 -diisopropylcarbodiimide to afford (N3N)Zr[η2(N,N)-(CyN)2dCPPh2] (7), (N3N)Zr[η2(N,N)-(PhN)2CPPh2] (8), and (N3N)Zr[η2(N,N)(iPrN)2CPPh2] (9) in 79, 93, and 96% yields, respectively (eq 4). Phosphaguanidinate ligands have been known for decades for a variety of metals.21 Each carbodiimide insertion product displays pseudo-C3v symmetry in the 1H NMR spectrum, and each gave diagnostic features in the IR, 13C NMR, and 31P NMR spectra that are summarized in Table 3. The spectral data suggested that the phosphaguanidinate ligand engages in η2 binding through the nitrogen atoms to the zirconium center. X-ray-quality crystals of 9 were grown from concentrated ethereal solutions cooled to -30 °C over extended periods. The molecular structure of 9, shown in Figure 3, is trigonal bipyramidal like, featuring an η2 phosphaguanidinate ligand bound though both nitrogen atoms of the carbodiimide as anticipated. The CdN bond lengths of the phosphaguanidinate ligand (Table 4) suggest a delocalized π bonding. This structure is consistent with known (21) (a) Ambrosius, H. P. M. M.; Van Der Linden, A. H. I. M.; Steggerda, J. J. J. Organomet. Chem. 1981, 204 (2), 211–220. (b) Thewissen, D. H. M. W.; Ambrosius, H. P. M. M.; Van Gaal, H. L. M.; Steggerda, J. J. J. Organomet. Chem. 1980, 192 (1), 101–113. (c) Grundy, J.; Mansfield, N. E.; Coles, M. P.; Hitchcock, P. B. Inorg. Chem. 2008, 47 (7), 2258–2260. (d) Mansfield, N. E.; Coles, M. P.; Avent, A. G.; Hitchcock, P. B. Organometallics 2006, 25 (10), 2470–2474. (e) Mansfield, N. E.; Coles, M. P.; Hitchcock, P. B. Dalton Trans. 2005, No. 17, 2833– 2841.

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Table 3. Selected 13C and 31P NMR Signals and IR Stretches for Carbodiimide Insertion Products 7-9 C δ(CdN) (JPC, Hz) Pδ νCN (cm-1) 13 31

7

8

9

152.3 (32) -18.5 1589

179.6 (63) -18.3 1594

175.5 (75) -9.1 1583

Figure 4. Molecular structure of 11 with thermal ellipsoids drawn at the 35% level. Hydrogen atoms are omitted for clarity.

Figure 3. Molecular structure of 9 with thermal ellipsoids drawn at the 35% level. Hydrogen atoms are omitted for clarity. Table 4. Selected Bond Lengths (A˚) and Angles (deg) for Complex 9 Zr-N(5) Zr-N(6) C(16)-P

N(5)-C(16)-N(6) N(5)-C(16)-P

2.304(1) 2.346(1) 1.913(1)

112.63 127.18

Zr-N(1) Zr-N(2) Zr-N(3) Zr-N(4) N(6)-C(16)-P

2.132(1) 2.138(1) 2.112(1) 2.542(1)

isothiocyanate resulted in the formation of (N3N)Zr[η2(N,S)-SC(PPh2)N(C10H7)] (10) as analytically pure, yellow microcrystals in 75% yield (eq 5). The 1H NMR spectrum is consistent with pseudo-C3 symmetry with respect to the triamidoamine ligand. At ambient temperature, two broad resonances corresponding to the methylene groups of the triamidoamine ligand are observed. This broadening suggests a dynamic process in the complex on the NMR time scale. An increase in the NMR temperature to 335 K results in resolved peaks as triplets at δ 2.99 and 2.27, respectively. The steric bulk of the napthyl group suggests that this process may be partial dissociation of an η2-bound phosphathiourea ligand. The phosphathiourea carbon was assigned at δ 204 as a doublet, with JPC = 55 Hz in the 13C NMR spectrum. Both 31P NMR and infrared spectroscopy were consistent with the formula given.

120.12

phosphaguanidinate complexes of zirconocene derivatives reported by Hey-Hawkins. In those instances, insertion of a carbodiimide into a Zr-P bond yielded the phosphaguanidinate product.14a,22 The phosphorus center is non-planar with a P-C bond length that implies there is no delocalization of the phosphorus lone pair into the N-C-N π system. This is an important consideration, given the interest in the interaction of the phosphorus with the N-C-N unit of a phosphaguanidene.23 The X-ray crystal structure of 9 appears to be the first six-coordinate zirconium complex bearing the N3N ligand. Six-coordinate zirconium complexes are significant, because reported bond-forming catalysis involving the (N3N)Zr fragment has been suggested to proceed via six-coordinate transition states.1c

Unsymmetrical heterocumulenes have also been shown to insert into Zr-P bonds. Reaction of 3 with 1-naphthyl

Reaction of 3 with phenyl isocyanate resulted in the formation of (N3N)Zr[η2(N,O)-OC(PPh2)N(Ph)] (11) as analytically pure light orange crystals in 56% yield. Spectroscopic data were consistent with other heterocumulene insertion products (vide infra). Single crystals of 11 suitable for an X-ray diffraction study were grown from a concentrated ethereal solution kept at -30 °C for extended periods. The solid-state structure of 11, shown in Figure 4, reveals η2 coordination of the phosphaurea ligand featuring Zr-O = 2.251(1) and Zr-N(5)=2.341(1) A˚ for the η2-bound phosphaurea ligand (Table 5). The bond lengths of both CdN (1.313(2) A˚) and CdO (1.300(2) A˚) are typical of CdN and CdO bonds, consistent with a delocalized bonding. Carbon-sulfur double bonds have also been shown to insert into Zr-P bonds. Reaction of 3 with carbon disulfide resulted in the 1,2-insertion product (N3N)Zr[η2-S2C(PPh2)] (22) Hey-Hawkins, E.; Lindenberg, F. Z. Naturforsch., B: Chem. Sci. 1993, 48, 951–957. (23) Mansfield, N. E.; Grundy, J.; Coles, M. P.; Avent, A. G.; Hitchcock, P. B. J. Am. Chem. Soc. 2006, 128 (42), 13879–13893.

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Table 5. Selected Bond Lengths (A˚) and Angles (deg) for Complex 11 Zr-N(5) Zr-O P-C(16)

C(29)-P-C(23) C(29)-P-C(16)

2.341(1) 2.251(1) 1.878(2)

102.02(8) 100.83(7)

Zr-N(1) Zr-N(2) Zr-N(3) Zr-N(4) C(23)-P-C(16)

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Table 6. Catalytic Data for the Hydrophosphination of Terminal Alkynes and Carbodiimidesa

2.117(1) 2.108(1) 2.087(1) 2.463(1) 103.80(7)

1

(12) as analytically pure red crystals in 76% yield. The H and 31P NMR and IR spectra were unremarkable. However, the S-C-S carbon was observed at δ 144 as a doublet with JPC =38 Hz in the 13C NMR spectrum.

Catalytic Hydrophosphination. The ease with which unsaturated organic molecules were able to insert into zirconiumphosphorus bonds of 1-3 provided an opportunity to investigate hydrophosphination catalysis with these zirconium complexes. Terminal alkynes were converted to vinyl phosphines, using complex 3 as a catalyst. Reaction of phenylacetylene and diphenylphosphine in the presence of 5 mol % of complex 3 were run at 100 °C in the dark for extended periods, affording vinyl phosphine products in 66% yield as a mixture of cis and trans alkenes in a 6:1 ratio, as determined by 31P NMR spectroscopy in comparison to literature data (Table 6).24 Similarly, 1-hexyne and diphenylphosphine were reacted with 5 mol % of complex 3 at 120 °C in the dark for extended periods to afford vinyl phosphine products in 56% yield as a mixture of the cis and trans alkenes in a 1:5 ratio, now favoring the trans product as compared to the literature data (Table 6).25 For both reactions, cis and trans vinyl phosphines were formed exclusively as anti-Markovnikov products, and no geminal phosphine products were detected. A range of other substrates possessing unsaturated C-C bonds was also tested. Reactions with electronic-rich and -deficient alkenes and internal alkynes failed to give hydrophosphination products at elevated temperatures and extended reaction times. While a number of unsaturated small molecules insert into the Zr-P bond of this family of complexes (vide supra), attempts at the catalytic hydrophosphination of ketones and nitriles also failed under the conditions tested. The limited ability to generalize the catalysis to at least internal alkynes suggested that two mechanisms are possible. The first mechanism is based on insertion of the substrate into the Zr-P bond that is due to the relative ease of this process stoichiometrically, and the second mechanism is based on the direct addition of the P-H bond across the CtC bond of an activated alkyne. The latter mechanism appeared to be possible on the basis of the observation of (24) (a) Hayashi, M.; Matsuura, Y.; Watanabe, Y. J. Org. Chem. 2006, 71 (24), 9248–9251. (b) Takaki, K.; Koshoji, G.; Komeyama, K.; Takeda, M.; Shishido, T.; Kitani, A.; Takehira, K. J. Org. Chem. 2003, 68 (17), 6554–6565. (25) Semenzin, D.; Etemad-Moghadam, G.; Albouy, D.; Diallo, O.; Koenig, M. J. Org. Chem. 1997, 62 (8), 2414–2422.

substrate

temp (°C)

time (h)

yield (%)b

phenylacetylene 1-hexyne CyNdCdNCy PhNdCdNPh i PrNdCdNiPr

100 120 120 120 120

67 72 24 24 7

66 56 75 70 53

a All runs at 5 mol % of complex 3 as catalyst in benzene-d6 solution in a PTFE-valved NMR tube. b Determined by 31P NMR spectroscopy.

previously reported alkynyl complexes (N3N)ZrCtCPh (13) or (N3N)ZrCtCBu via 1H NMR spectroscopy during the catalytic reactions.19 This potential of direct addition was further implied by reports of hydrophosphination catalysis where the metal did not participate in the P-C bond-forming step.26 Interestingly, heterofunctionalization catalysts that do not directly involve the metal center in key bond-forming steps have been described for other systems.27 Thus, mechanistic insight was sought for the hydrophosphination of terminal alkynes. The presence of both complex 3 and terminal alkynyl complexes suggested an equilibrium process, which seemed unusual given the large difference in calculated bond energies between phosphido and alkynyl complexes of the (N3N)Zr fragment.19 An attempt to measure Keq for the interconversion of 3 and 13 with phenylacetylene and diphenylphosphine was performed by investigating each side of the equilibrium reaction (Scheme 1). Treatment of complex 13 with 1 equiv of phenylphosphine gave no obvious reaction, as observed by 1H or 31P NMR spectroscopy over a period of hours at ambient temperature in benzene-d6 solution. However, reaction of complex 3 with 1 equiv of phenylacetylene resulted in 84% conversion to 13 in with the appearance of vinyl phosphine products in 4% yield according to 1H and 31P NMR spectroscopy. These results suggest that reaction at the Zr-P bond is likely important and are not consistent with direct P-H addition across the CtC bond. The lack of reaction between 13 and diphenylphosphine suggested that formation of 3 is unfavorable, and deuterium labeling experiments were undertaken to better understand how the catalysis proceeds in the face of this apparent substrate inhibition. Reaction of 3 with phenylacetylene-d1 resulted in formation of 13-d1, where the deuterium label had been predominately incorporated in the trimethylsilyl substituents of the triamidoamine ligand, and a small amount of Ph2PD was observed. When 13 was treated with Ph2PD, 13-d1 was produced with concomitant formation of Ph2PH, as observed by 1H and 31P NMR spectroscopy in benzene-d6 solution (Scheme 2). This study implicates the existence of an equilibrium between the metalated complex [(Me3SiNCH2)2NCH2CH2NSiMe2CH2-κ5(N,N,N,N,C)]Zr (14) and diphenylphosphine or phenylacetylene in the formation of 3 and 13, respectively. Additionally, these labeling experiments demonstrate a high kinetic lability of the X- ligand from (N3N)ZrX complexes by formation of HX and 14. More germane to this study, the summation of these indirect lines of evidence argues for a mechanism based on insertion of substrate into the Zr-P bond. A reviewer suggested that the reaction could proceed via dehydrocoupling of alkyne and (26) Huang, J.-S.; Yu, G.-A.; Xie, J.; Wong, K.-M.; Zhu, N.; Che, C.-M. Inorg. Chem. 2008, 47 (20), 9166–9181. (27) Glaser, P. B.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125 (45), 13640–13641.

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Scheme 2. Deuterium Labeling Reactions

phosphine to yield Ph2PCtCR, which could then be hydrogenated by the H2 byproduct to give the observed vinylphosphine. The competition experiments do not seem to support this mechanism, which should not depend on which ligand (alkynyl or phosphido) is bound to zirconium. A catalytic run was conducted under reduced pressure (to thwart hydrogenation), which did not adversely effect the catalysis and the same vinylphosphine products were formed at the same qualitative rate. While this is not strong enough evidence to refute such a mechanism, the rarity of catalytic reactions involving bond formation to carbon by what appears to be σ-bond metathesis lead us to view this mechanistic suggestion with caution, given the current evidence supporting insertion (vide supra).28 With the information from the deuterium labeling studies as well as competition experiments, a mechanism of hydrophosphination is proposed on the basis of insertion of substrate into a Zr-P bond (Scheme 3). Elimination of the vinyl phosphine product occurs by metalation of the triamidoamine ligand to form complex 14. Reaction with diphenylphosphine completes the catalytic cycle with the formation of a phosphido complex (3). However, there is a competitive, nonproductive path in which 14 reacts with alkyne or complex 3 undergoes ligand exchange with alkyne via 14. It is the formation of stable, terminal alkynyl complexes that likely accounts for the sluggish overall catalysis. Although this mechanism describes the formation of vinyl phosphine products, it does not account for the selectivity for (28) (a) Dagorne, S.; Rodewald, S.; Jordan, R. F. Organometallics 1997, 16 (25), 5541–5555. (b) Guram, A. S.; Jordan, R. F. Organometallics 1991, 10 (10), 3470–3479. (c) Guram, A. S.; Jordan, R. F. J. Org. Chem. 1992, 57 (22), 5994–5999. (d) Guram, A. S.; Jordan, R. F.; Taylor, D. F. J. Am. Chem. Soc. 1991, 113 (5), 1833–1835. (e) Jordan, R. F.; Guram, A. S. Organometallics 1990, 9 (7), 2116–2123. (f) Jordan, R. F.; Taylor, D. F. J. Am. Chem. Soc. 1989, 111 (2), 778–779. (g) Jordan, R. F.; Taylor, D. F.; Baenziger, N. C. Organometallics 1990, 9 (5), 1546– 1557. (h) Rodewald, S.; Jordan, R. F. J. Am. Chem. Soc. 1994, 116 (10), 4491–4492. (i) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125 (26), 7971–7977. (j) Sadow, A. D.; Tilley, T. D. Angew. Chem., Int. Ed. 2003, 42 (7), 803–805. (k) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2005, 127 (2), 643–656.

Roering et al.

either the cis or trans alkene in the hydrophosphination of terminal alkynes. Further study would be required to establish the origin of the selectivity displayed by this particular catalyst. Other substrates are more efficiently hydrophosphinated by complex 3. Reactions of symmetrical carbodiimides and diphenylphosphine in the presence of 5 mol % of 3 at 120 °C in the dark afforded phosphaguanidine products in 53-75% yield. Phosphaguanidines are well-known due to both the biological relevance of the P-C-N functionality as well as their ability to be transition-metal ligands.29 Previous reports of phosphaguanidine formation from carbodiimides has shown the need for a catalyst, as control reactions were not facile even at elevated temperatures.30 However, the turnover frequencies of the calcium systems by Hill and co-workers are higher than those measured for complex 3 as a catalyst.8 It appears that carbodiimides represent a better substrate for the hydrophosphination catalysis by complex 3, likely because this substrate does not compete effectively with diphenylphosphine as a ligand. It is hypothesized that the hydrophosphination of carbodiimides undergoes a similar mechanism, where the carbodiimide substrate inserts into the Zr-P bond, as illustrated by the stoichiometric reactions.

Conclusion Triamidoamine-supported zirconium phosphido complexes are able to undergo a variety of insertion reactions with small, polar unsaturated substrates. The diphenylphosphido complex 3 has also been found to catalyze the hydrophosphination of terminal alkynes as well as carbodiimides to vinyl phosphines and phosphaguanidines, respectively. These appear to be the first early-transition-metal complexes that engage in insertion-based hydrophosphination catalysis, in contrast to the cycloaddition-based hydrophosphination catalysis with Ti reported by Mindiola.9 Despite this new development, these Zr catalysts are not as efficient in the hydrophosphination of carbodiimides as the calcium systems reported by Barrett and Hill.7,8 Current data support an insertion-based mechanism for these zirconium-based hydrophosphination catalysts.

Experimental Section General Considerations. All manipulations were performed under a nitrogen atmosphere with dry, oxygen-free solvents using an M. Braun glovebox or standard Schlenk techniques. Benzene-d6 was purchased from Cambridge Isotope Laboratory and then degassed and dried over NaK alloy. Celite-454 was heated to a temperature greater than 180 °C under dynamic vacuum for at least 8 h. Elemental analyses were performed on an Elementar Microcube. NMR spectra were recorded with either a Bruker AXR or Varian 500 MHz spectrometer in benzene-d6 and are reported with reference to residual solvent resonances (δ 7.16 and 128.0) or external 85% H3PO4 (δ 0.00). Infrared spectra were collected on a Perkin-Elmer System 2000 FT-IR spectrometer at a resolution of 1 cm-1. The starting materials 1-3 and N,N0 -diphenylcarbodiimide were prepared (29) (a) Grundy, J.; Coles, M. P.; Hitchcock, P. B. Dalton Trans. 2003, No. 12, 2573–2577. (b) Mansfield, N. E.; Coles, M. P.; Avent, A. G.; Hitchcock, P. B. Organometallics 2006, 25 (10), 2470–2474. (c) Hirai, T.; Han, L.-B. J. Am. Chem. Soc. 2006, 128 (23), 7422–7423. (30) Zhang, W.-X.; Nishiura, M.; Hou, Z. Chem. Commun. 2006, No. 36, 3812–3814.

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Scheme 3. Proposed Catalytic Cycle for the Hydrophosphination of Terminal Alkynes with Diphenylphosphine using a TriamidoamineSupported Zirconium Catalyst

according to literature procedures.19,31 Diphenylphosphine-d1 was prepared by reaction of D2O with lithium diphenylphenylphosphide in THF followed by distillation. Lithium diphenylphosphide was prepared by the reduction of triphenylphosphine with a copious excess of lithium metal in THF. Phenylacetylene-d1 was prepared by reaction of D2O with lithium phenylacetylide and distilled from Et2O under a nitrogen atmosphere. The lithium phenylacetylide was prepared by addition of 1 equiv of n-butyllithium to phenylacetylene in Et2O. All other chemicals were obtained from commercial suppliers and dried by conventional means. Preparation of (N3N)ZrNdCPh(PHCy) (4). A 50 mL roundbottom flask was charged with 2 (370 mg, 0.44 mmol), benzonitrile (67 mg, 0.44 mmol), and ca. 5 mL of benzene. To the stirred solution was added a 2 mL benzene solution containing benzonitrile. An instant color change from yellow to red was observed upon addition of benzonitrile to the zirconium solution, which was stirred at ambient temperature for ca. 3 h. The solution was frozen and lyophilized, yielding pink microcrystals of compound 4 (370 mg, 0.56 mmol, 86%). 1H NMR (500.1 MHz): δ 7.91 (dt, 2 H, Ph), 7.19 (d, 1 H, Ph), 7.09 (d, 2 H, Ph), 4.47 (dd, JPH=224 Hz, JHH=7 Hz, 1 H, PH), 3.35 (m, 6 H, CH2), 2.45 (m, 6 H, CH2), 2.02 (m, 2 H, C6H11), 1.59 (m, 2 H, C6H11), 1.47 (m, 1 H, C6H11), 1.20-1.28 (m, 4 H, C6H11), 1.11 (m, 2 H, C6H11), 0.23 (s, 27 H, CH3). 13C{1H} NMR (125.8 MHz): δ 187.5 (d, CdN, JPC =28 Hz), 144.6 (d, C6H5, JPC =32 Hz), 130.0 (s, C6H5), 128.5 (s, C6H5), 128.3 (s, C6H5), 127.1 (s, C6H5), 127.0 (s, C6H5), 62.1 (s, CH2), 47.4 (s, CH2), 35.4 (s, C6H11), 33.9 (d, JPC = 12 Hz, C6H11), 32.7 (d, JPC = 20 Hz, C6H11), 27.5 (s, C6H11), 27.4 (s, C6H11), 26.3 (s, C6H11), 1.8 (s, CH3). 31P{1H} NMR (202.4 MHz): δ -4.1. IR (KBr, Nujol): 2308 m (νPH), 1610 s (νCN), 1593 m, 1575 m, 1463 s, 1448 s, 1377 m 1266 m, 1239 s, 1194 m, 1144 w, 1074 s, 1057 s, 930 s, 903 m, 836 s, 783 s, 707 w, 676 w, 565 m cm-1. Anal. Calcd for C28H56N5PSi3Zr: C, 50.25; H, 8.43; N, 10.46. Found: C, 50.49; H, 8.46; N, 10.34. Preparation of (N3N)ZrNdCPh(PPh2) (5). A 50 mL roundbottom flask was charged with 3 (50 mg, 0.079 mmol) and ca. 5 mL of benzene. To the stirred solution was added benzonitrile (8.1 mg, 0.079 mmol), and the resultant red solution was stirred at ambient temperature for 48 h; then the benzene was lyophilized, yielding purple microcrystals of compound 5 (42 mg, 0.057 mmol, 72%). 1H NMR (500.1 MHz): δ 7.99 (d, C6H5, 1 H), 7.67 (t, C6H5, 2 H), 7.06-6.93 (m, C6H5, 12 H), 3.22 (t, CH2, (31) (a) Covert, K. J.; Mayol, A.-R.; Wolczanski, P. T. Inorg. Chim. Acta 1997, 263 (1-2), 263–278. (b) Gudat, D.; Verkade, J. G. Organometallics 1989, 8 (12), 2772–2779. (c) Fell, J. B.; Coppola, G. M. Synth. Commun. 1995, 25 (1), 43–7.

6 H), 2.43 (t, CH2, 6 H), 0.17 (s, CH3, 27 H). 13C{1H} NMR (125.8 MHz): δ 144.9 (d, CdN, JPC=38.6 Hz), 136.5 (d, C6H5, JPC=10.8 Hz), 135.9 (d, C6H5, JPC=10.8 Hz), 129.5 (s, C6H5), 128.9 (s, C6H5), 128.8 (s, C6H5), 128.7 (s, C6H5), 128.6 (s, C6H5), 61.3 (s, CH2), 47.8 (s, CH2), 1.9 (s, CH3). 31P{1H} NMR (202.4 MHz): δ 24.5 (s). IR (KBr, Nujol): 1630 s (νCN), 1460 s, 1378 m, 1261 s, 1242 s, 1192 w, 1074 s, 1054 s, 1026 m, 936 s, 920 m, 907 m, 836 s, 786 s, 772 s, 742 s, 693 s, 634 m, 600 s, 578 w, 546 w, 498 m, 447 w cm-1. Anal. Calcd for C34H54N5PSi3Zr: C, 55.24; H, 7.36; N, 9.47. Found: C, 55.34; H, 7.48, N, 9.18. Preparation of (N3N)ZrOCMe2(PHPh) (6). A 50 mL roundbottom flask was charged with 1 (50 mg, 0.093 mmol) and ca. 5 mL of benzene. With stirring, acetone (9.7 mg, 0.093 mmol) in 2 mL of benzene was added to the zirconium solution, resulting in an instantaneous color change from red to colorless. The solution was stirred at ambient temperature for 48 h, and then the benzene was lyophilized, yielding colorless microcrystals of compound 6 (42 mg, 0.057 mmol, 95%). 1H NMR (500.1 MHz): δ 7.50 (s, 2 H, C6H5), 7.05 (s, 3 H, C6H5), 4.61 (d, JPH=206 Hz, 1 H, PH), 3.24 (m, 6 H, CH2), 2.35 (m, 6 H, CH2), 1.71 (d, JHH= 39 Hz, 3 H, CH3), 1.70 (d, JHH=49 Hz, 3 H, CH3), 0.36 (s, 27 H, CH3). 13C{1H} NMR (125.8 MHz): δ 137.6 (d, JPC = 19 Hz, C6H5), 135.8 (d, JPC=15 Hz, C6H5), one phenyl resonance was not observed and presumed to be obstructed by benzene-d6 solvent, 80.1 (s, CH3), 63.9 (s, CH2), 46.2 (s, CH2), 34.2 (s, CH2), 31.2 (d, JPC=29 Hz, (CH3)2C-P), 1.8 (s, CH3). 31P{1H} NMR (202.4 MHz): δ -7.3. IR (KBr, Nujol): 2302 w (νPH), 1467 s, 1374 s, 1244 s, 1180 m, 1143 m, 1026 s, 925 s, 833 s cm-1. Anal. Calcd for C30H55N4OPSi3Zr: C, 46.60; H, 8.32; N, 9.06. Found: C, 46.60; H, 8.55; N, 8.93. Preparation of (N3N)ZrNH(PPh2)(CPh2)] (7). A 1 mL Et2O solution of 3 (50 mg, 0.079 mmol) was cooled to -30 °C, and to that solution was added a cold 1 mL Et2O solution of benzophenone imine (14 mg, 0.079 mmol). After 1 h, the resulting dark orange solution was dried under reduced pressure. The residue was dissolved in Et2O, and the solution was filtered and then concentrated under reduced pressure. The solution was then cooled to -30 °C, yielding dark orange crystals that were collected in several crops and dried under reduced pressure (41 mg, 0.050 mmol, 64%). Characterization data for 7 have already been reported.19 1H NMR (500.1 MHz): δ 7.30 (m, C6H5, 4 H), 7.11 (m, C6H5, 6 H), 3.49 (t, C6H5, 6 H), 2.58 (t, CH2, 6 H), 0.26 (s, CH3, 27 H). 13C{1H} NMR (125.8 MHz): δ 174.8 (s, CdN), 142.1 (s, C6H5), 133.9 (s, C6H5), 129.3 (s, C6H5), 128.5 (s, C6H5), 61.4 (s, CH2), 47.1 (s, CH2), 1.4 (s, CH3). 31P{1H} NMR (202.4 MHz): δ 47.9 (s). IR (KBr, Nujol): 1641 s (νCN), 1595 w, 1463 s, 1378 m, 1258 s, 1242 s, 1080 s, 1020 m, 931 s, 901 m, 837 s, 784 s, 741 m, 701 m, 631 m, 564 m, 478 w, 451 w cm-1.

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General Preparation for Carbodiimide Insertions. A 50 mL round-bottom flask was charged with 3 (50 mg, 0.079 mmol) and ca. 5 mL of benzene. To the stirred solution was added the corresponding carbodiimide N,N0 -dicylohexylcarbodiimide (17 mg, 0.079 mmol), N,N0 -diphenylcarbodiimide (15 mg, 0.079 mmol), or N,N0 -diisopropylcarbodiimide (10 mg, 0.079 mmol) in ca. 2 mL of benzene. A color change was observed for each insertion product. The solutions were stirred at ambient temperature for 4-14 h when the flask was then placed in the freezer and the benzene was lyophilized, yielding the title compound. Preparation of (N3N)Zr[η2(N,N)-(NCy)2(PPh2)] (8). A color change from red to light yellow was seen instantly upon addition of carbodiimide solution to the phosphido complex, and the solution was stirred at ambient temperature for 4 h. The benzene solution was lyophilized, yielding the title compound as a light yellow powder (0.052 g, 0.044 mmol, 79%). 1H NMR (500.1 MHz): δ 7.68 (t, 3 H, C6H5), 7.05 (m, 2 H, Ph), 3.79 (m, 2 H, C6H11), 3.30 (t, 6 H, CH2), 2.50 (t, 6 H, CH2), 1.86 (m, 8 H, C6H11), 1.65 (m, 4 H, C6H11), 1.49 (m, 2 H, C6H11), 1.17 (m, 2 H, C6H11), 1.04 (m, 4 H, C6H11), 0.40 (s, 27 H, CH3). 13C{1H} NMR (125.8 MHz): δ 152.3 (d, JPC=31.5 Hz, CdN), 135.8 (d, JPC =14.6 Hz, C6H5), 134.3 (d, JPC =18.6 Hz, C6H5), 129.3 (s, C6H5), 129.0 (d, JPC=5.3 Hz, C6H5) 68.3 (s, CH2), 60.4 (d, JPC= 32.8 Hz, C6H11), 49.3 (s, CH2), 35.8 (s, C6H11), 32.6 (s, C6H11), 26.3 (d, JPC =25.7 Hz, C6H11), 25.3 (s, C6H11), 24.6 (s, C6H11), 2.9 (s, CH3). 31P{1H} NMR (202.4 MHz): δ -18.5 (s). IR (KBr, Nujol): 1589 (νCN) m, 1480 m, 1366 w, 1343 w, 1243 s, 1218 s, 1100 s, 1026 m, 974 m, 888 m, 846 w, 741 s, 697 s, 624 w, 523 m, 492 m, 478 m cm-1. Anal. Calcd for C40H71N6PSi3Zr: C, 57.03; H, 8.49; N, 9.98. Found: C, 57.49; H, 8.52; N, 9.21. Preparation of (N3N)Zr[η2(N,N)-(PhN)2C(PPh2)] (9). A color change from red to light yellow was seen instantly upon addition of carbodiimide solution to the phosphido complex, and the solution was stirred at ambient temperature for 14 h. The benzene solution was lyophilized, yielding the title compound as a yellow powder (60 mg, 0.079 mmol, 93%). 1H NMR (500.1 MHz): δ 7.51 (m, 4 H, C6H5), 7.32 (m, 4 H, C6H5), 6.90 (m, 4 H, C6H5), 6.85 (m, 4 H, C6H5), 6.80 (m, 2 H, C6H5), 6.67 (m, 2 H, C6H5), 3.32 (t, 6 H, CH2), 2.39 (t, 6 H, CH2), 0.27 (s, 27 H, CH3). 13 C{1H} NMR (125.8 MHz): δ 179.6 (d, JPC = 63 Hz, CdN), 147.0 (s, C6H5), 135.0 (d, JPC =22 Hz, C6H5), 134.5 (s, C6H5), 128.2 (s, C6H5), 125.6 (s, C6H5), 122.9 (s, C6H5), 63.2 (s, CH2), 47.2 (s, CH2), 1.9 (s, CH3), two phenyl resonances were not observed and presumed to be obscured by benzene-d6 solvent. 31 P{1H} NMR (202.4 MHz): δ -18.3 (s). IR (KBr, Nujol): 2849 s, 1594 (νCN) m, 1492 m, 1456 s, 1365 s, 1244 m, 1203 m, 1171 w, 1078 m, 1046 w, 1026 w, 940 m, 906 w, 837 s, 784 s, 746 m, 695 m, 676 w, 581 w, 510 w cm-1. Anal. Calcd for C40H59N6PSi3Zr: C, 57.86; H, 7.16; N, 10.12. Found: C, 57.66; H, 7.19; N, 9.91. Preparation of (N3N)Zr[η2(N,N)-(iPrN)2C(PPh2)] (10). A gradual color change from red to colorless was observed upon stirring for 1 h. The solution was stirred a total of 14 h at ambient temperature. The benzene solution was lyophilized, yielding the title compound as a colorless powder (58 mg, 0.076 mmol, 96%). 1H NMR (500.1 MHz): δ 7.74 (m, 4 H, C6H5), 7.16 (m, C6H5) (accurate integration could not be obtained because of overlap with benzene-d6 solvent), 7.06 (t, 2 H, C6H5), 4.26 (m, 2 H, CH), 3.26 (t, 6 H, CH2), 2.48 (t, 6 H, CH2), 1.24 (d, 12 H, CH3), 0.37 (s, 27 H, CH3). 13C{1H} NMR (125.8 MHz): δ 175.5 (d, JPC=72 Hz, CdN), 135.1 (d, JPC=18 Hz, C6H5), 133.8 (d, JPC=20 Hz, C6H5), 128.5 (s, C6H5), 128.3 (d, JPC= 6 Hz, C6H5), 64.5 (s, CH2), 49.8 (d, JPC=11 Hz, CH), 47.4 (s, CH2), 25.6 (d, JPC=4 Hz, CH3), 3.2 (s, CH3). 31P{1H} NMR (202.4 MHz): δ -9.10 (s). IR (KBr, Nujol): 1946 w, 1583 (νCN) w, 1462 w, 1377 w, 1290 w, 1246 m, 1215 w, 1180 m, 1120 s, 1026 m, 936 s, 841 s, 783 w, 741 m, 695 w, 585 m, 551 w cm-1. Preparation of (N3N)Zr[η2(N,S)-SC(PPh2)N(C10H7)] (11). A 1 mL Et2O solution of 3 (50 mg, 0.079 mmol) was cooled to -30 °C, and to that solution was added a cold 1 mL Et2O solution of 1-naphthyl isothiocyanate (15 mg, 0.079 mmol). After 1 h, the resulting light yellow solution was dried under reduced pressure.

Roering et al. The residue was dissolved in Et2O, and the solution was filtered and then concentrated under reduced pressure until incipient crystallization. The solution was warmed to dissolve the crystals, and the solution was then cooled to -30 °C. Yellow crystals were collected in several crops and dried under vacuum (48 mg, 0.059 mmol, 75%). 1H NMR (500.1 MHz, 338 K): δ 8.38 (d, C6H5, 1 H, JPC =8.3 Hz), 7.49 (m, C6H5, 5 H), 7.36 (m, C6H5, 2 H), 7.31 (t, C6H5, 2 H), 7.23 (m, C6H5, 3 H), 7.00 (m, C6H5, 4 H), 2.99 (t, CH2, 6 H), 2.27 (t, CH2, 6 H), 0.41 (s, CH3, 27 H). 13 C{1H} NMR (125.8 MHz): δ 204.5 (d, CdN, JPC =55.5 Hz), 146.1 (d, Ar, JPC = 8.8 Hz), 135.3 (s, Ar), 135.1 (s, Ar), 134.3 (s, Ar), 129.3 (s, C6H5), 128.7 (s, Ar), 126.1 (s, Ar), 125.6 (s, Ar), 125.3 (s, Ar), 125.1 (s, Ar), 121.6 (s, Ar), 121.5 (s, Ar), three phenyl resonances obscured by benzene-d6 solvent, 63.3 (s, CH2), 48.0 (s, CH2), 2.5 (s, CH3). 31P{1H} NMR (202.4 MHz): δ 0.7 (s). IR (KBr, Nujol): 1592 w, 1575 w, 1480 s, 1458 s (νCN), 1378 m, 1259 m, 1069 m, 1054 m, 1028 m, 936 s, 912 m, 898 w, 839 s, 794 m, 772 s, 747 m, 724 w, 700 w, 687 w, 665 w, 548 w, 496 w, 468 w, 421 w cm-1. Anal. Calcd for C38H56N5SPSi3Zr: C, 55.56; H, 6.87; N, 8.53. Found: C, 53.85; H, 6.95; N, 7.82. Preparation of (N3N)Zr[η2(N,O)-OC(PPh2)NPh] (12). A 1 mL Et2O solution of 3 (50 mg, 0.079 mmol) was cooled to -30 °C, and to that solution was added a cold 1 mL Et2O solution of phenyl isocyanate (9.4 mg, 0.079 mmol). After 1 h, the resulting light orange solution was dried under reduced pressure. The residue was redissolved in Et2O, and the solution was filtered through Celite and then concentrated under reduced pressure. The solution was then cooled to -30 °C. Light orange crystals were collected in several crops and dried under reduced pressure (34 mg, 0.044 mmol, 56%). 1 H NMR (500.1 MHz): δ 7.73 (t, C6H5, 4 H), 7.30 (d, C6H5, 2 H, JPC=7.5 Hz), 7.08 (t, C6H5, 4 H), 7.01 (t, C6H5, 4 H), 6.76 (t, C6H5, 1 H), 3.26 (t, CH2, 6 H), 2.39 (t, CH2, 6 H), 0.18 (s, CH3, 27 H). 13 C{1H} NMR (125.8 MHz): δ 186.9 (d, CdN, JPC=43 Hz), 145.0 (s, C6H5), 132.0 (s, C6H5), 135.7 (s, C6H5), 132.8 (d, JPC =6 Hz, C6H5), 129.4 (s, C6H5), 128.5 (s, C6H5), 128.4 (s, C6H5), 124.2 (s, C6H5), 61.9 (s, CH2), 47.8 (s, CH2), 1.9 (s, CH3). 31P{1H} NMR (202.4 MHz): δ -12.1 (s). IR (KBr, Nujol): 2923 s, 2854 s, 1959 w (νCO), 1579 m, 1502 s, 1464 s, 1277 m, 1242 m, 1214 w, 1060 w, 940 m, 837 m, 693 w, 518 w, 496 w cm-1. Anal. Calcd for C22H44N5OSi3Zr: C, 54.07; H, 7.21; N, 9.27. Found: C, 54.35; H, 7.18; N, 9.20. Preparation of (N3N)Zr[η2-CS2(PPh2)] (13). A 1 mL Et2O solution of 3 (50 mg, 0.079 mmol) was cooled to -30 °C, and to that solution was added a cold 1 mL Et2O solution of carbon disulfide (6.0 mg, 0.079 mmol). After 1 h, the resulting red solution was dried under vacuum. The residue was dissolved in Et2O, and the solution was filtered through Celite and concentrated under reduced pressure. The solution was then cooled to -30 °C, at which point red crystals were collected in several crops and dried under vacuum (43 mg, 0.060 mmol, 76%). 1H NMR (500.1 MHz): δ 7.91 (t, C6H5, 2 H), 7.90 (t, C6H5, 2 H), 7.261 (t, C6H5, 3 H), 7.22 (m, C6H5, 2 H), 3.43 (t, CH2, 3 H), 3.35 (t, CH2, 3 H), 2.40-2.36 (m, CH2, 3 H), 0.43 (s, CH3, 27 H). 13 C{1H} NMR (125.8 MHz): δ 144.9 (d, C-P, JPC =38.6 Hz), 136.5 (d, C6H5, JPC =10.8 Hz), 135.9 (d, C6H5, JPC =10.8 Hz), 129.5 (s, C6H5), 128.9 (s, C6H5), 128.8 (s, C6H5), 128.7 (s, C6H5), 128.6 (s, C6H5), 61.3 (s, CH2), 47.8 (s, CH2), 1.9 (s, CH3). 31 P{1H} NMR (202.4 MHz): δ 45.9 (s). IR (KBr, Nujol): 2925 s, 2855 s, 1579 m, 1460 s, 1376 m, 1299 w, 1263 m, 1244 s, 1143 w, 1048 s, 1019 m, 927 s, 892 w, 837 s, 781, 743 s, 696 m, 567 w, 463 w cm-1. Anal. Calcd for C28H50N4PS2Si3Zr: C, 47.15; H, 7.07; N, 7.85. Found: C, 46.73; H, 7.16; N, 7.81. Catalytic Hydrophosphination. Phenylacetylene. A PFTEvalved NMR tube was charged with 3 (10 mg, 0.016 mmol), diphenylphosphine (59 mg, 0.31 mmol), phenylacetylene (32 mg, 0.31 mmol), and benzene-d6 (500 μL). The tube was shielded from light and placed in a 100 °C oil bath for 67 h. The reaction gave cis and trans vinyl phosphine products in a 4:1 mixture of the anti-Markovnikov product on the basis of 31P NMR spectroscopy. The vinyl phosphines have been reported previously.24

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Table 7. Crystal Data and Structure Refinement Parameters for Complexes 4, 5, 9, and 11 4

5

formula C28H56N5PSi3Zr C34H54N5PSi3Zr 669.24 739.28 Mr cryst syst monoclinic triclinic a/A˚ 12.3884(7) 10.1235(4) b/A˚ 15.0561(9) 12.0108(5) c/A˚ 19.166(1) 17.5314(8) R/deg 90 88.382(1) β/deg 94.313(1) 87.427(1) γ/deg 90 69.172(1) 3564.8(4) 1990.2(1) V/A˚3 P1 space group P21/n Z 4 2 θ range/deg 1.72-30.47 1.81-28.28 0.479 0.435 μ/mm-1 N 49 628 26 287 10 263 9812 Nind 0.0298 0.0220 Rint a 0.0257 0.0275 R1 (I > 2σ(I)) b wR2 (I > 2σ(I)) 0.0606 0.0689 0.415, -0.197 0.588, -0.528 ΔFmax, ΔFmin/e A˚3 GOF on R1 1.044 1.028 P P P P a R1 = ||Fo| - |Fc||/ |Fo|. b wR2 = { [w(Fo2 - Fc2)2]/ w(Fo2)2]}1/2.

1-Hexyne. A PFTE-valved NMR tube was charged with 3 (10 mg, 0.016 mmol), diphenylphosphine (59 mg, 0.31 mmol), 1-hexyne (25 mg, 0.031 mmol), and benzene-d6 (500 μL). The tube was shielded from light and placed in a 120 °C oil bath for 72 h. The reaction gave cis and trans vinyl phosphine products on the basis of 31P NMR spectroscopy. The vinyl phosphines have been reported previously.25 Carbodiimides. A PFTE-valved NMR tube was charged with 3 (10 mg, 0.016 mmol), diphenylphosphine (59 mg, 0.314 mmol), RNdCdNR (R=Cy, 65 mg; R=Ph, 59 mg; R= iPr, 40 mg; 0.31 mmol), and benzene-d6, (500 μL). The tube was heated at 120 °C for 12-24 h. Phosphaguanidine products were observed in 75, 84, and 53% yields for R=Cy, Ph, iPr, respectively, on the basis of 31P NMR spectroscopy. The phosphaguanidine products match previously reported products.8 Competition Experiments. PTFE-valved NMR tube was charged with (N3N)ZrCtCPh (20 mg, 0.036 mmol), diphenylphosphine (6.7 mg, 0.036 mmol), and a benzene-d6 (500 μL) solution containing ferrocene as an internal standard (0.01 M). A second PTFE-valved NMR tube was charged with 3 (23 mg, 0.036 mmol), phenylacetylene (3.7 mg, 0.036 mmol), and ferrocene standard benzene-d6 (500 μL). Both NMR tubes were shielded from light and placed in a 70 °C oil bath for a given amount of time. Deuterium Labeling Studies. A PTFE-valved NMR tube was charged with 13 (0.010 g, 0.018 mmol), diphenylphosphine-d1 (0.0034 g, 0.0181 mmol), and benzene-d6 (500 μL). Ferrocene was dissolved in the benzene-d6 and used as an internal standard. The solution was shielded from light and reacted. Both 1H and 31P NMR spectra were taken at regular intervals to monitor the progress of the reaction. A second PTFE-valved NMR tube was charged with 3 (0.010 g, 0.016 mmol), phenylacetylene-d1 (0.0017 g, 0.016 mmol), and benzene-d6 (500 μL). Ferrocene was dissolved in the benzene-d6 and used as an internal standard. The solution was shielded

9

11

C34H63N6PSi3Zr 762.36 triclinic 9.887(1) 11.625(2) 18.429(2) 99.906(2) 99.369(2) 98.168(2) 2026.9(5) P1 2 1.14-28.28 0.430 26 576 10 003 0.0230 0.0256 0.0615 0.424, -0.255 1.031

C34H54N5OPSi3Zr 755.28 triclinic 10.0233(4) 10.7297(5) 19.9437(9) 76.0090(1) 76.3280(1) 70.6970(1) 1935.39(2) P1 2 2.04-28.28 0.451 25 455 9553 0.0235 0.0290 0.0716 1.044, -0.601 1.036

from light and reacted. Both 1H and 31P NMR spectra were taken at regular intervals to monitor the progress of the reaction. X-ray Structure Determinations. X-ray diffraction data were collected on a Bruker APEX 2 CCD platform diffractometer (Mo KR, λ=0.710 73 A˚) at 125 K. Suitable crystals of complexes 4, 5, 9, and 11 were mounted on nylon loops with Paratone-N cryoprotectant oil. The structures were solved using direct methods and standard difference map techniques and were refined by full-matrix least-squares procedures on F2 with SHELXTL (version 6.14).32 All non-hydrogen atoms were refined anisotropically. Hydrogen atoms on carbon were included in calculated positions and were refined using a riding model. The hydrogen atom on the phosphorus of (N3N)ZrNd CPh(PHCy) (4), H(1), was located in the Fourier difference map and refined freely. Crystal data and structure refinement parameters are given in Table 7.

Acknowledgment. This work was supported by the U.S. National Science Foundation (Grant No. CHE-0747612) and the donors of the Petroleum Research Fund, administered by the American Chemical Society (No. 466669G3). Summer support for S.M.C. was provided by the ACS Project SEED and the Green Mountain ACS Local Section. X-ray crystallographic facilities were provided by the U.S. National Science Foundation (Grant No. CHE-0521237 to J.M.T.). R.W. is a Research Fellow of the Alfred P. Sloan Foundation. Supporting Information Available: CIF files giving crystal data for 4, 5, 9, and 11. This material is available free of charge via the Internet at http://pubs.acs.org. (32) Sheldrick, G. M. Acta Crystallogr. 2008, A64 (1), 112–122.