Reactivity Studies of a T-Shaped Yttrium Carbene: C–F and C–O

(d) Mills , D. P.; Cooper , O. J.; Tuna , F.; McInnes , E. J. L.; Davies , E. S.; McMaster , J.; Moro , F.; Lewis , W.; Blake , A. J.; Liddle , S. T. ...
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Reactivity Studies of a T‑Shaped Yttrium Carbene: C−F and C−O Bond Activation and CC Bond Formation Promoted by [Y(BIPM)(I)(THF)2] (BIPM = C(PPh2NSiMe3)2) David P. Mills, William Lewis, Alexander J. Blake, and Stephen T. Liddle* School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, U.K. S Supporting Information *

ABSTRACT: The yttrium carbene complex [Y(BIPM)(I)(THF)2] (1; BIPM = C(PPh2NSiMe3)2) was reacted with a range of unsaturated substrates. The reaction of 1 with the phosphaalkyne PCBut afforded the [2 + 2] cycloaddition product [Y{C(PPh2NSiMe3)2(PCBut)-κ4C,C′,N,N′}(I)] (2). Similarly, the reactions of 1 with the heteroallenes N,N′-dicyclohexylcarbodiimide and tert-butyl isocyanate gave the [2 + 2] cycloaddition products [Y{C(PPh 2 NSiMe 3 ) 2 [C(NCy) 2 ]-κ 4 C,N,N′,N″}(I)(THF)] (3) and [Y{C(PPh2NSiMe3)2[C(O)(NBut)]-κ4C,N,N′,O}(I)(THF)2] (4), respectively. In contrast, the reaction of 1 with tert-butyl isothiocyanate afforded the ketenimine ButNCC(PPh2NSiMe3)2 (5), with the concomitant formal elimination of “YSI(THF)n”. The sterically demanding arylamine 2,6diisopropylphenylamine reacted with 1 via a 1,2-addition across the YC bond to yield the anilide−methanide complex [Y(BIPMH)(NHDipp)(I)(THF)] (6; Dipp = C6H3Pri2-2,6). The reaction of 1 with the benzopyrone coumarin affords the ring-opened dinuclear aryloxide−enolate complex [Y2{C(PPh2NSiMe3)2[C(O)(CHCHC6H4O-2)]-κ2N,O:μ,κ-O′}2(I)(μ-I)(THF)] (7), which is postulated to form by sequential Y−O, C−C, and CC bond formation and cleavage of the C−O ester linkage and the CO and YC double bonds. Benzoyl fluoride reacts with 1 to afford 1/2 equiv of the bis-enolate complex [Y{C(PPh2NSiMe3)2[C(O)(Ph)]-κ2N,O}2(I)] (8) with formal elimination of “YF2I(THF)n” by ligand scrambling. Complexes 2−8 have been characterized by X-ray crystallography, multielement NMR spectroscopy, FTIR spectroscopy, and CHN microanalyses.

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INTRODUCTION The field of f-block carbene chemistry is poorly developed in comparison to transition-metal carbene chemistry, which has been investigated extensively as a consequence of the synthetic utility of these systems.1 Most of the previously reported f-block carbene chemistry in the literature is that of dative, Lewis basic N-heterocyclic carbenes,2 but there are considerably fewer examples of f-block carbene complexes that are not derived from stable free carbenes.3 This can be attributed to the energetic mismatch of the relevant frontier orbitals of the formal LnC or AnC double bond, which makes the preparation of such complexes synthetically challenging. However, the highly polarized bonding in these systems promises interesting reactivities.4 It is noteworthy that the modest amount of covalency in the MC double bond of early-metal carbene complexes has led to them being more commonly referred to as geminal methanediides, which may be a more appropriate description of the bonding in these systems.5 The most successful strategy that has been employed to overcome the inherent instability of LnC or AnC linkages is the use of bulky phosphorus(V) substituents, such as in bis(diphenylthiophosphinoyl)carbenes, {C(PPh2S)2}2−, and bis(diphenyliminophosphorano)carbenes, {C(PPh2NR)2}2−, (e.g., BIPM, R = SiMe3).3 The importance of the phosphorus © 2013 American Chemical Society

substituents in stabilizing molecular mononuclear lanthanide and actinide carbenes is illustrated by the formation of polymetallic clusters with bridging methylidene fragments in their absence.6 Cavell was the first to report a bis(phosphorus-stabilized) lanthanide carbene complex in 2000, namely [Sm(BIPM)(NCy2)(THF)], by the double deprotonation of the parent methane with the homoleptic complex samarium(III) tris(dicyclohexylamide).7 This synthetic route required forcing conditions, and perhaps as a consequence no reactivity studies have been reported for [Sm(BIPM)(NCy2)(THF)] to date. More recently, Le Floch and co-workers prepared a neodymium(III) carbene with a related ligand framework, [Nd{C(PPh2NPri)2}{HC(PPh2NPri)2}], by unusually facile deprotonation of the methanide precursor [Nd{HC(PPh2NPri)2}2(I)] with potassium bis(trimethylsilyl)amide, but no reactivity studies have been reported.8 Le Floch, Nief, and Mézailles employed salt metathesis methodologies to prepare the lanthanide bis(diphenylthiophosphinoyl)carbene complexes [Ln{C(PPh2S)2}(μ-I)(THF)2]2 Special Issue: Recent Advances in Organo-f-Element Chemistry Received: October 29, 2012 Published: February 12, 2013 1239

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(Ln = Sm, Tm)9 and [Li(THF)4]][Ln{C(PPh2S)2}2] (Ln = Sm, Tm)10 from samarium(III) or thulium(III) triiodide. The neutral lanthanide carbenes were found to react rapidly with benzophenone to afford the expected alkene Wittig product, Ph2CC(PPh2S)2, whereas the anionic carbenes were found to react more sluggishly, with the “open” metallo-oxetane intermediates [Ln{C(PPh2S)2(Ph2CO)}2{Li(THF)}] (Ln = Sm, Tm) isolated from the reaction mixture. Mézailles and Ephritikhine have reported the mononuclear lithium-free uranium(IV) bis(diphenylthiophosphinoyl)carbene complexes, namely [U{C(PPh2S)2}2(py)2], [U{C(PPh2S)2}(Cp)2] (Cp = C5H5) and [U{C(PPh2S)2}(BH4)2(THF)2], which were formed form salt metathesis reactions employing the borohydride precursor [U(BH4)4].11 The salt metathesis methodology was extended by Berthet, Cantat, Mézailles, and Ephritikhine to prepare the first uranyl(VI) carbene, [UO2{C(PPh2S)2}(py)2], from [UO2(OTf)2].12 Initial reactivity studies of these uranium(IV) and uranyl(VI) bis(diphenylthiophosphinoyl)carbene complexes with ketones and aldehydes have led exclusively to the isolation of the expected alkene Wittig products.11,12 In 2008 we reported the yttrium alkyl carbene complex [Y(BIPM)(CH2SiMe3)(THF)], which is prepared by the facile double deprotonation of the methane precursor H2C(PPh2NSiMe3)2 (BIPMH2) by [Y(CH2SiMe3)3(THF)2].13 The mild synthesis of [Y(BIPM)(CH2SiMe3)(THF)] is in contrast to the forcing conditions required to prepare [Sm(BIPM)(NCy2)(THF)]7 and provides a rare opportunity to investigate the reactivity of the YC double bond. The isolation of [Y(BIPM)(CH2SiMe3)(THF)] allowed for the first time a comparison of Ln−Calkyl and LnCcarbene bonds, and DFT analysis of the bonding suggests a predominantly electrostatic YC bond, with the HOMO and HOMO-2 principally describing the lone pairs at the methanediide center and the HOMO-1 primarily representing the Y−Calkyl bond.13 Following the synthesis of [Y(BIPM)(CH2SiMe3)(THF)], we reported the synthesis of the related lanthanide carbenes [Ln(BIPM)(CH2Ph)(THF)] (Ln = Y;14 Ln = Dy, Er15) and [Ln(BIPM)(I)(THF)2] (Ln = Y (1);16,17 Ln = Er17), which were also synthesized by double-deprotonation strategies from yttrium alkyl precursors. The solid-state structure of 1 revealed that the BIPM ligand adopts a flat, T-shaped geometry at the methanediide center, which is in contrast to the typical pseudo-boat conformation adopted by the yttrium alkyl carbene systems, thus warranting further investigation.17 However, DFT analysis of [Y(BIPM)(CH2Ph)(THF)] and 1 revealed frontier orbital manifolds similar to those of [Y(BIPM)(CH2SiMe3)(THF)], which differ principally in their frontier orbital ordering.14,17 Therefore, although the ligand framework of 1 has maximized its potential for increased covalency by being in an ideal geometry for orbital overlap, it does not display appreciable differences in its bonding to [Y(BIPM)(CH2SiMe3)(THF)] and [Y(BIPM)(CH2Ph)(THF)]. The double deprotonation of BIPMH2 by lanthanide benzyls was extended to larger lanthanides, but it was found that in these cases the coordination sphere was large enough to allow a single deprotonation of a second molecule of BIPMH2 to afford [Ln(BIPM)(BIPMH)] (Ln = La, Ce, Pr, Nd, Sm, Gd).15 It was later found that salt elimination reactions are more appropriate to access BIPM complexes for the larger lanthanides, such as in [La{C(PPh2NMes)2}(I)(THF)3] (Mes = C6H2Me3-2,4,6).18 These synthetic methodologies were also employed by us to prepare uranium(IV), -(V) and -(VI) carbene derivatives of bis(diphenyliminophosphorano)methanediides, which display

greater covalency than 1 and its congeners, and they typically react with ketones and aldehydes to liberate the anticipated alkene Wittig products.19 We reported a preliminary reactivity study of [Y(BIPM)(CH2Ph)(THF)] in 2009.14 The reaction of [Y(BIPM)(CH2Ph)(THF)] with diphenyldiazene afforded [Y(BIPM){N(Ph)N(Ph)(CH2Ph-κ2N,N′)}] by a 1,2-migratory insertion of azobenzene into the Y−Calkyl bond, and no reactivity was observed at the YCcarbene bond even when another 1 equiv of diphenyldiazene was added. The reaction of [Y(BIPM)(CH2Ph)(THF)] with benzophenone similarly furnished [Y(BIPM){OC(CH2Ph)Ph2}(THF)] by a 1,2-migratory insertion into the Y−Calkyl bond, and the addition of a further 1 equiv of benzophenone afforded the bridging methanediide dimer [Y(μ-BIPM){OC(CH2Ph)Ph2}]2 on heating the reaction mixture, with no alkene Wittig products observed. It is noteworthy that the generated bridging methanediide product does not incorporate an extra 1 equiv of benzophenone, but its formation is directly proportional to the quantity of benzophenone added. The reactivity of 1 was first reported in 2009, when it was generated in situ by the deprotonation of [Y(BIPMH)(I)2(THF)] with benzylpotassium and reacted with the gallium(I) heterocycle [K(tmeda)][Ga{N(Dipp)ArCH}2] (Dipp = C6H3Pri2-2,6, tmeda = N,N,N′,N′-tetramethylethylenediamine)20 to yield [Y(BIPM){Ga[N(Dipp)CH]2}(THF)2]. This complex exhibits the first structurally characterized Ga−Y bond16 and is notable, as there few f-element metal−metal bonds in the literature.21 A preliminary reactivity study of 1 was reported in tandem with an initial reactivity study of [Y(BIPM)(CH2SiMe3)(THF)],22 the latter of which was shown to react sequentially with 3 equiv of benzophenone to afford first [Y(BIPM){OC(CH2SiMe3)Ph2}(THF)] by a 1,2migratory insertion into the Y−Calkyl bond and then the yttrium methanide alkoxide [Y(BIPMH){OC(CH 2SiMe 3 )Ph 2 }O{(CPh2)(OCPh)C6H4}], which is coordinated by a substituted isobenzofuran. In this reaction, regioselective activation of an ortho phenyl proton of benzophenone by the YC bond occurs to generate the methanide, and the generated carbanion reacts at the ketyl carbon of a second molecule of benzophenone to form a C−C bond, which then undergoes an intramolecular rearrangement to form a C−O bond. In contrast, 1 was shown to react with 2 equiv of benzophenone to give the oxymethylbenzophenone-coordinated yttrium methanide complex [Y(BIPMH){OCPh(C6H4)-2-C(O)Ph2}(I)] (Scheme 1), which was converted to the substituted isobenzofuran complex by a salt metathesis reaction with [KOC(CH2SiMe3)Ph2]. The wider applicability of 1 in effecting the activation of ketones was explored, with the reaction of 1 with 2 equiv of PhCOBut generating the diastereomeric substituted isobenzofuran complex [Y(BIPMH)O{(CPhBut)(OCBut)C6H4}(I)] directly, with no oxymethylbenzophenone-coordinated intermediate isolated. 1 reacts with the enolizable ketone PhCOMe to furnish a substituted cyclohexene dypnopinacol, which is formed by C−H activation at the α-methyl group of the ketone and then undergoes cyclotetramerization and dehydration, which again is in contrast to the reactivity of transition-metal carbene complexes with enolizable ketones.23 The nonclassical reactivity of 1 and [Y(BIPM)(CH2SiMe3)(THF)] with ketones prompted us to further investigate the reactivity of lanthanide carbenes with unsaturated substrates. Herein, we report the reactivity of 1 with heteroallenes, amines, cyclic esters, acyl halides and tert-butylphosphaalkyne. 1240

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2 is postulated to form by the initial side-on coordination of the phosphaalkyne, which is preferred to end-on coordination for these species due to the π character of their HOMO.25 This would then be followed by nucleophilic attack of a lone pair of the methanediide of 1 to form a C−P bond, with the triple bond of the alkyne converting to an alkene to allow the formation of a new polarized Y−C bond. [2 + 2] cycloaddition reactions of phosphaalkynes are relatively rare,25 and head-to-tail cycloadditions at metal centers are scarce.26 Germane to this point, the Schrock alkylidenes [M(CHBut)(NDipp)(OR)2] (M = Mo, R = CMe(CF3)2, CMe2(CF3); M = W, R = CMe(CF3)2) react with ButCP to afford the carbenes [M{CHButP(OR)C(But)-κ2C,C′}(NDipp)(OR)] (M = Mo, R = CMe(CF3)2, CMe2(CF3); M = W, R = CMe(CF3)2) as major products, which form via a [2 + 2] cycloaddition reaction followed by a 1,3-migration of an alkoxide from the metal center to phosphorus.26a,b Other notable examples of head-to-tail [2 + 2] cycloaddition reactions of ButCP include the reaction between ButCP and [Ti(Cp*)2(CCH2)] (Cp* = C5Me5) to form [Ti(Cp*)2{C(P)(CCH2)(But)-κ2C,P}], where a head-totail isomer was detected by NMR spectroscopy,26c and the reaction between ButCP, ButNH2 and [Ti(Cp)(Cl)3], where a head-to-tail intermediate forms during the formation of [Ti(Cp)(Cl){P(NBut)(CHBut)(NHBut)-κ2C,N].26d The 31P{1H} NMR spectrum of 2 in d8-THF exhibits a broad resonance at δ −72.23 ppm and a doublet at δ 1.62 ppm (2JPP = 13.0 Hz). The broad signal at high field is assigned as the phosphalkene-P(III) center and is comparable to that observed for [Mo{CHBut P[OCMe(CF 3) 2]C(But )-κ2C,C′}(NDipp){OCMe(CF3)2}] (δ −105.7 ppm [C6D6]).26a No 2JPP coupling

Scheme 1. Previously Reported Reactions of 1 with Aryl Ketones

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RESULTS AND DISCUSSION Treatment of 1 with ButCP24 afforded the 1-phospha-3metallacyclobutene product [Y{C(PPh2NSiMe3)2(PCBut)κ4C,C′,N,N′}(I)] (2), following a [2 + 2] cycloaddition reaction, in 14% crystalline yield (Scheme 2). The low yield is a reflection of the high solubility of 2; indeed, derivatives of 1 are generally very soluble, often resulting in low crystalline yields, whereas inspection of the crude reaction mixtures by NMR spectroscopy suggests that in all the reactions reported here the isolated compounds represent the major products. Scheme 2. Synthesis of 2−8

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statistically indistinguishable but compare favorably with the corresponding distances observed for [Mo{CHButP[OCMe(CF3)2]C(But)-κ2C,C′}(NDipp){OCMe(CF3)}] (P−C(av) = 1.822(9) Å)26a and [Ti(Cp*)2{C(P)(CCH2)(But)-κ2C,P}] (PC = 1.701(5) Å).26c In common with the reaction of 1 with ButCP, treatment of 1 with the heteroallenes N,N′-dicyclohexylcarbodiimide and tertbutyl isocyanate gave the [2 + 2] cycloaddition products [Y{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N″}(I)(THF)] (3) and [Y{C(PPh 2 NSiMe 3 ) 2 [C(O)(NBu t )]-κ 4 C,N,N′,O}(I)(THF)2] (4), respectively, each in 54% crystalline yield (Scheme 2). The formation of 3 is analogous to the preparation of [Zr{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N″}(Cl)2] and [Hf{C(PPh2NSiMe3)2[C(NAr)2]-κ4C,N,N′,N″}(Cl)2] (Ar = p-tolyl).27 In contrast, the formation of 4 differs from the synthesis of [M{C(PPh2NSiMe3)2[C(O)(NAd)]-κ4C,N,N′,N″}(Cl)2] (M = Zr, Hf, Ad = adamantyl, C10H15),27 wherein the heteroallene forms M−N bonds upon cycloaddition, rather than the Y−O bond formed in 4. We suggest this differing [2 + 2] cycloaddition behavior reflects the increased preference for O-donor ligands in early metals. The 31P{1H} NMR spectra of 3 and 4 exhibit doublet resonances with identical coupling constants (3, δ 16.57 ppm, 2JYP = 3.2 Hz; 4, δ 20.39, 2JYP = 3.2 Hz); these are downfield of the resonance for 1, which also exhibits a greater 2JYP value (1, δ 3.48 ppm, 2JYP = 13.0 Hz),17 but are comparable to that of [Zr{C(PPh2NSiMe3)2[C(NCy)2]κ4C,N,N′,N″}(Cl)2] (δ 21.0 ppm).27 The methanide carbons of 3 and 4 resonate as the expected triplet of doublets in their respective 13C{1H} NMR spectra (3, δ 20.71 ppm, JPC = 102.7 Hz, JYC = 2.3 Hz; 4, δ 31.39 ppm, JPC = 111.9 Hz, JYC = 2.3 Hz), with chemical shifts and coupling constants that are typical for yttrium bis(iminophosphorano)methanide complexes16,22,29 and [Zr{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N″}(Cl)2] (δ 15.5 ppm, JPC = 96.0 Hz).27 The former heteroallene quaternary carbons of 3 and 4 also exhibit coupling with the two 31P nuclei (3, δ 153.15 ppm, dd, 2JPC = 6.1 Hz, 3.8 Hz; 4, δ 156.26 ppm, t, 2 JPC = 2.8 Hz) that is comparable in magnitude to that observed for [Zr{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N″}(Cl)2] (δ 148.7 ppm, bt, 2JPC = 4 Hz).27 The solid-state structures of 3 and 4 were determined by X-ray crystallography (Figures 2 and 3; selected bond lengths and angles are compiled in Table 1). In common with 2 and [Zr{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N″}(Cl)2],27 the four-coordinate, dianionic ligands of 3 and 4 exhibit a propeller-shaped geometry with N(1), N(2), and N(3) (3) or N(1), N(2), and O(1) (4) at the vertices of an approximate triangle. The coordination sphere of the yttrium centers are completed by an iodide and one (3) or two (4) THF ligands, which presumably reflects the varying steric demands of the organic ligand frameworks in 3 and 4. Both complexes exhibit bond lengths and angles that are typical for early-metal bis(iminophosphorano)methanides and Y−Cmethanide distances (3, Y(1)−C(1) 2.644(8) Å; 4, 2.676(3) Å) that are comparable to those in other closely related yttrium methanides.16,22,29 The C(32)−N(3) (1.393(10) Å) and C(32)−N(4) (1.276(10) Å) distances of 3 and the corresponding C(32)−O(1) (1.338(3) Å) and C(32)−N(3) (1.274(3) Å) distances of 4 indicate localized single and double bonds, respectively, as was reported for [Zr{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N″}(Cl)2] (C−N = 1.384(5) and 1.285(5) Å).27 As expected, the Y(1)−N(3) amide distance of 3 (2.267(7) Å) and the Y(1)−O(1) alkoxide distance of 4 (2.2133(19) Å) are shorter than the other Y−N and Y−O bond lengths in these complexes and are statistically invariant to,

constant could be extracted from this resonance, due to the broad nature of the signal; however, this coupling was resolved in the second resonance, which corresponds to the imino-P(V) centers. No methanide or phosphaalkene resonances could be observed in the 13C{1H} NMR spectrum of 2, which we attribute to extensive JPC and JYC couplings reducing the intensity of these signals to baseline values. The quaternary carbon of the tert-butyl group is observed as a doublet at δ 28.81 ppm (2JPC = 6.0 Hz), which is similar to those observed for [Mo{CHBu tP[OCMe(CF 3) 2]C(Bu t)-κ2 C,C′}(NDipp){OCMe(CF3)2}] (δ 33.3 and 33.4 ppm, 2JPC = 18 and 15 Hz [C6D6]).26a The molecular structure of 2 is illustrated in Figure 1, and selected bond lengths and angles are given in Table 1.

Figure 1. Molecular structure of 2 with selective atom labeling. Displacement ellipsoids are set at 40% probability, and hydrogen atoms are omitted for clarity. Symmetry operation to generate the complete structure: x, − y + 3/2, z.

The tetradentate ligand framework in 2 is dianionic and propeller-shaped and exhibits three essentially planar fused four-membered metallocycles: two PNCY and one PC2Y. The crystal structure of 2 exhibits exact Cs symmetry, whereby a mirror plane intersects C(1), Y(1), I(1), P(2), and C(17), with two PNCY rings oriented 50.1(6)° to the mirror plane. The iodide ligand is trans to the methanide center (C(1)−Y(1)− I(1) = 176.0(6)°) and resides in a pocket approximately equidistant between the CMe3 and SiMe3 groups. The distances and angles within the six-membered CP2N2Y assembly are unremarkable, as is the Y(1)−C(1) distance (2.556(16) Å), which is statistically indistinguishable from that observed for [Y(BIPMH)(I)2(THF)] (Y−C 2.599(2) Å).16 The N(1)− Y(1)−N(1A) bite angle (116.7(6)°) is comparable to the corresponding angle in [Zr{C(PPh2NSiMe3)2[C(NCy)2]κ4C,N,N′,N″}(Cl)2] (N−Zr−N = 120.0(1)°).27 The Y(1)− C(17) distance of 2 (2.36(3) Å) is notably short, residing toward the lower end of the range of reported Y−C distances (2.124−3.135 Å), and is comparable to previously reported YC bonds (2.356−2.422 Å).28 The P(2)−C(1) (1.82(2) Å) and P(2)−C(17) (1.71(2) Å) bond distances of 2 are 1242

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Table 1. Selected Bond Lengths (Å) and Angles (deg) for 2−8 6·C4H8O

2 Y(1)−C(1) Y(1)−N(1) C(1)−P(1) C(17)−P(2) N(1)−Y(1)−N(1A) P(2)−C(17)−Y(1) C(17)−P(2)−C(1) P(1)−C(1)−P(2)

2.556(16) 2.305(11) 1.761(11) 1.71(2) 116.7(6) 96.8(11) 105.9(11) 116.4(7)

Y(1)−C(1) Y(1)−N(1) Y(1)−N(3) C(1)−P(1) P(1)−N(1) C(1)−C(32) C(32)−N(4) N(1)−Y(1)−N(2) N(2)−Y(1)−N(3) P(2)−N(2)−Y(1) N(2)−P(2)−C(1) P(1)−C(1)−C(32) C(1)−C(32)−N(3) C(32)−C(1)−Y(1) P(2)−C(1)−Y(1)

2.644(8) 2.375(6) 2.267(6) 1.742(7) 1.600(7) 1.550(10) 1.276(10) 96.8(2) 109.1(2) 97.9(3) 108.0(4) 112.6(5) 108.6(6) 86.7(4) 84.1(3)

Y(1)−C(17) Y(1)−I(1) C(1)−P(2) P(1)−N(1) P(1)−N(1)−Y(1) N(1)−P(1)−C(1) P(1)−C(1)−P(1A) C(1)−Y(1)−I(1)

2.36(3) 2.937(2) 1.82(2) 1.633(10) 96.9(5) 108.8(7) 125.7(14) 176.0(6)

3 Y(1)−I(1) Y(1)−N(2) Y(1)−O(1) C(1)−P(2) P(2)−N(2) C(32)−N(3) N(1)−Y(1)−N(3) P(1)−N(1)−Y(1) N(1)−P(1)−C(1) P(1)−C(1)−P(2) P(2)−C(1)−C(32) C(32)−N(3)−Y(1) P(1)−C(1)−Y(1)

3.0284(9) 2.351(6) 2.407(5) 1.758(7) 1.601(7) 1.393(10) 95.9(2) 98.3(3) 110.2(4) 122.9(4) 122.6(5) 107.0(5) 85.4(3)

4 Y(1)−C(1) Y(1)−N(1) Y(1)−O(1) Y(1)−O(3) C(1)−P(2) P(2)−N(2) C(32)−N(3) N(1)−Y(1)−N(2) N(2)−Y(1)−O(1) P(2)−N(2)−Y(1) N(2)−P(2)−C(1) P(1)−C(1)−C(32) C(1)−C(32)−O(1) C(32)−C(1)−Y(1) P(2)−C(1)−Y(1)

2.676(3) Y(1)−I(1) 2.417(2) Y(1)−N(2) 2.2133(19) Y(1)−O(2) 2.5170(19) C(1)−P(1) 1.744(3) P(1)−N(1) 1.610(2) C(1)−C(32) 1.274(3) C(32)−O(1) 99.76(8) N(1)−Y(1)−O(1) 100.10(7) P(1)−N(1)−Y(1) 98.98(10) N(1)−P(1)−C(1) 109.82(12) P(1)−C(1)−P(2) 116.49(19) P(2)−C(1)−C(32) 111.9(2) C(32)−O(1)−Y(1) 83.09(14) P(1)−C(1)−Y(1) 84.71(10) 5·0.5C7H8

C(1)−C(32) C(1)−P(1) P(1)−N(1) N(1)−P(1)−C(1) P(1)−C(1)−P(2) P(2)−C(1)−C(32)

1.322(4) 1.809(3) 1.535(2) 115.32(12) 122.09(14) 118.8(2)

C(32)−N(3) C(1)−P(2) P(2)−N(2) N(2)−P(2)−C(1) P(1)−C(1)−C(32) C(1)−C(32)−N(3)

3.0539(4) 2.359(2) 2.4427(19) 1.733(3) 1.610(2) 1.524(3) 1.338(3) 101.06(7) 98.10(10) 109.70(12) 126.35(15) 114.60(18) 107.85(15) 86.07(10)

1.207(3) 1.809(3) 1.532(2) 113.45(12) 118.23(19) 172.9(3)

or longer than, the terminal amide and alkoxide distances, respectively, found in the complexes [Y(BIPMH)(NPh)2] (2.264(2) Å mean)29a and [Y(BIPM){OC(CH2SiMe3)Ph2}(THF)] (2.037(10) Å).22 With 3 prepared, we investigated the analogous reaction of 1 with tert-butyl isothiocyanate. However, instead of forming the anticipated [2 + 2] cycloaddition product, the Wittig product compound ButNCC(PPh2NSiMe3)2 (5) was isolated in 22% crystalline yield, presumably with concomitant formal elimination of “YSI(THF)n” (Scheme 2). This reactivity is unusual, given that the yttrium center of 1 is extremely oxophilic and does not effect a similar reaction with tert-butyl isocyanate.

Y(1)−C(1) Y(1)−N(1) Y(1)−N(3) C(1)−P(1) P(1)−N(1) N(1)−Y(1)−N(2) P(2)−N(2)−Y(1) N(2)−P(2)−C(1) Y(1)−N(3)−C(36)

2.619(6) Y(1)−I(1) 2.414(5) Y(1)−N(2) 2.232(5) Y(1)−O(1) 1.756(6) C(1)−P(2) 1.605(5) P(2)−N(2) 93.18(17) P(1)−N(1)−Y(1) 98.5(2) N(1)−P(1)−C(1) 107.6(3) P(1)−C(1)−P(2) 159.0(4) 7·3.25C7H8

2.9865(6) 2.417(5) 2.386(4) 1.755(6) 1.607(5) 99.0(2) 106.1(3) 123.0(3)

Y(1)−I(2) Y(1)−O(1) Y(1)−O(3) Y(1)···C(31) C(1)−P(2) P(2)−N(2) C(32)−O(1) C(33)−C(34) Y(2)−I(2) Y(2)−O(2) Y(2)−O(5) C(45)−P(3) P(3)−N(3) C(45)−C(76) C(76)−C(77) Y(1)−O(2)−Y(2) Y(1)−I(2)−Y(2) N(2)−P(2)−C(1) C(1)−C(32)−O(1) Y(2)−N(4)−P(4) P(4)−C(45)−C(76) C(76)−O(4)−Y(2)

3.1990(6) Y(1)−N(2) 2.158(4) Y(1)−O(2) 2.333(4) Y(1)−O(5) 3.075(8) C(1)−P(1) 1.792(6) P(1)−N(1) 1.622(5) C(1)−C(32) 1.311(7) C(32)−C(33) 1.340(8) Y(2)−I(1) 3.1915(6) Y(2)−N(4) 2.294(4) Y(2)−O(4) 2.308(4) Y(2)···C(74) 1.801(6) C(45)−P(4) 1.546(5) P(4)−N(4) 1.386(8) C(76)−O(4) 1.469(8) C(77)−C(78) 101.74(13) Y(1)−O(5)−Y(2) 67.339(14) Y(1)−N(2)−P(2) 113.8(2) P(2)−C(1)−C(32) 119.9(5) C(32)−O(1)−Y(1) 120.0(2) N(4)−P(4)−C(45) 112.9(4) C(45)−C(76)−O(4) 127.2(4) 8·1.5C7H8

2.330(5) 2.273(3) 2.236(4) 1.795(6) 1.540(5) 1.400(8) 1.476(8) 2.9572(6) 2.391(4) 2.146(4) 3.308(8) 1.789(6) 1.615(5) 1.309(7) 1.328(9) 102.43(15) 121.1(2) 111.8(4) 123.4(3) 113.4(3) 119.1(5)

Y(1)−I(1) Y(1)−O(2) Y(1)−N(3) Y(1)···C(65) C(1)−P(2) P(2)−N(2) C(32)−O(1) C(39)−P(4) P(4)−N(4) C(70)−O(2) Y(1)−N(1)−P(1) P(1)−C(1)−C(32) Y(1)−N(3)−P(3) P(3)−C(39)−C(70)

3.0406(5) 2.145(3) 2.412(4) 3.548(7) 1.804(5) 1.539(4) 1.310(5) 1.795(4) 1.548(4) 1.311(5) 121.2(2) 113.8(3) 113.86(19) 111.7(3)

2.125(3) 2.384(4) 3.038(8) 1.810(4) 1.607(4) 1.374(7) 1.819(4) 1.607(4) 1.378(6)

Y(1)−O(1) Y(1)−N(1) Y(1)···C(28) C(1)−P(1) P(1)−N(1) C(1)−C(32) C(39)−P(3) P(3)−N(3) C(39)−C(70) N(1)−P(1)−C(1) C(1)−C(32)−O(1) N(3)−P(3)−C(39) C(39)−C(70)−O(2)

112.0(2) 122.7(4) 115.04(19) 121.7(4)

It is noteworthy that a [2 + 2] cycloaddition reaction has been implicated in the reaction of a titanium alkylidene with tert-butyl isocyanate,30 and to the best of our knowledge there is only one example in the literature of a desulfurization of isocyanates mediated by a metal-bound carbene.31 The novel ketenimine 5 gives a characteristic strong absorption at 2048 cm−1 in the FTIR spectrum, resulting from stretching modes of the CCN moiety, which compares well to those for the P(III) diphosphinoketenimine ButNCC(PPh2)2 (ν(CCN) 2030 and 2002 cm−1 (in CH2Cl2)).32 In the 13C{1H} NMR spectrum of 5 the former methanediide carbon was observed at δ 55.86 ppm (t, JPC = 100.3 Hz) and the central carbon of the 1243

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Figure 4. Molecular structure of 5·0.5C7H8 with selective atom labeling. Displacement ellipsoids are set at 40% probability, and hydrogen atoms and lattice solvent are omitted for clarity. Figure 2. Molecular structure of 3 with selective atom labeling. Displacement ellipsoids are set at 40% probability, and hydrogen atoms are omitted for clarity.

mutually cis and trans to the CC bond. The C(1)−C(32) (1.322(4) Å) and C(32)−N(3) (1.207(3) Å) distances and almost linear C(1)−C(32)−N(3) angle of 5 (172.9(3)°) are comparable to the corresponding distances and angles observed for [Cu{C(PPh2O)2(CNBut)-κ2-O,O}2(BF4)][BF4] (CC = 1.346(4) Å, CN = 1.175(4) Å, CNC = 173.8(4)°).32 All other bond lengths and angles in 5 are unremarkable.33 The reaction of 1 with 2,6-diisopropylphenylamine proceeds via a 1,2-addition across the YC bond to yield the anilide− methanide complex [Y(BIPMH)(NHDipp)(I)(THF)] (6) in 59% crystalline yield after workup (Scheme 2). This reactivity was also observed for the complex [Hf(BIPM)(Cl)2], which was shown to react with p-tolylamine to give [Hf(BIPMH)(NHC6H4Me-4)(Cl)2].27 The 31P{1H} NMR spectrum of 6 (d8-THF) exhibited a doublet resonance at δ 19.17 ppm (2JYP = 6.5 Hz), which is comparable to those in 3, 4, and other closely related complexes.16,22,29 The signal arising from the NH group was observed in the 1H NMR spectrum of 6 (d8-THF) at δ 4.59 ppm, which is upfield of that reported for [Hf(BIPMH)(NHC6H4Me-4)(Cl)2] (δ 6.46 ppm (C6D6))27 but is comparable to the value reported for the related yttrium pyridyl-1-azaallyl−anilide [Y{(C 6 H 3 Pri 2 -2,6)NC(Me)CH(C5H3N-1,SiMe2CH2-2)-κ3C,N,N′}(NHDipp)(THF)] (δ 4.75 ppm (C6D6)).34 Similarly, the resonance of the methanide proton of 6 (δ 1.26 ppm) is upfield of that observed for [Hf(BIPMH)(NHC6H4Me-4)(Cl)2] (δ 2.36 ppm (C6D6))27 but is comparable to those for other yttrium bis(iminophosphorano)methanide complexes.16,22,29 The expected triplet of doublets corresponding to the methanide carbon atom was observed in the 13C{1H} NMR spectrum of 6 (δ 17.91 ppm, JPC = 87.5 Hz, JYC = 4.5 Hz) but cannot be compared to the 13 C{1H} NMR spectrum of [Hf(BIPMH)(NHC6H4Me-4)(Cl)2], as this has not been reported.27 However, the resonance for the anilide ipso carbon at δ 151.99 ppm (d, 2JYC = 3.0 Hz) compares well to the corresponding value reported for [Y{(C 6 H 3 Pr i 2 -2,6)NC(Me)CH(C 5 H 3 N-1,SiMe 2 CH 2 -2)κ3C,N,N′}(NHDipp)(THF)] (δ 151.8 ppm (C6D6)).34

Figure 3. Molecular structure of 4 with selective atom labeling. Displacement ellipsoids are set at 40% probability, and hydrogen atoms and lattice solvent are omitted for clarity.

ketenimine at δ 162.63 ppm (t, 2JPC = 5.9 Hz). A single resonance is observed in the 31P{1H} NMR spectrum at δ −2.58 ppm in C6D6 (cf. δ −10.5 ppm in CD2Cl2 observed for ButNC C(PPh2)2).32 The molecular structure of 5·0.5C7H8 was determined by X-ray crystallography and is illustrated in Figure 4; selected bond lengths and angles can be found in Table 1. 5 exhibits a geometry similar to those of the analogous Wittig products Ph(H)CC(PPh2NSiMe3)219b and R(H)CC(PPh2NSiMe3)2 (R = 9-anthracene),19d with the two NSiMe3 substituents 1244

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“methanide−alkoxide” intermediate. This then rearranges by breaking the Y−C and ester linkages to generate the CC double bond and the “aryloxide−enolate” product. An absorption is observed in the FTIR spectrum of 7 (ν 1627 cm−1) which is assigned as the CC functional group. The 31P{1H} NMR spectrum of 7 exhibits two doublet resonances (δ 4.91 and 28.32 ppm, 2JPP = 37.3 Hz), indicative of inequivalent iminophosphorano arms of the ligand scaffold as a result of one being coordinated and the other being pendant. The 1H and 13C{1H} NMR spectra of 7 are complex as a result of the highly asymmetric coordination environment (see below) apparently persisting in THF solution, which is additionally evidenced by the low solubility of 7 in d6-benzene. However, the spectra are readily assigned and noteworthy resonances are observed in the 13C{1H} NMR spectrum of 7 for the low-field O-bound enolate carbon (δ 184.75 ppm, dd, 2JPC = 13.6 and 3.5 Hz) and the former methanediide carbon (δ 98.60 ppm, dd, JPC = 119.7 and 91.6 Hz), which couple to the two inequivalent 31P nuclei. The aryloxide ipso carbon resonates as a doublet at δ 162.31 ppm (2JYC = 6.0 Hz), which is similar to the corresponding value reported for [Y(ODipp)3(THF)2] (δ 157.92 ppm, 2JYC = 5.0 Hz).37 The molecular structure of 7·3.25C7H8 is illustrated in Figure 6, and selected bond lengths and angles are given in

The molecular structure of 6·C4H8O was determined and is illustrated in Figure 5, with selected bond lengths and angles

Figure 5. Molecular structure of 6·C4H8O with selective atom labeling. Displacement ellipsoids are set at 40% probability, and hydrogen atoms (except amide and methanide hydrogens) and lattice solvent are omitted for clarity.

given in Table 1. The bis(iminophosphorano)methanide framework adopts an open-book conformation,3b,c with a Y−C distance (2.619(6) Å) that is characteristic of complexes of this class.16,22,27 The Y(1)−N(3) distance (2.232(5) Å) and nonlinear Y(1)−N(3)−C(36) angle (159.0(4)°) of 6 are similar to the corresponding values observed for [Y{(C6H3Pri2-2,6)NC(Me)CH(C5H3N-1,SiMe2CH2-2)-κ3-C,N,N′}(NHDipp)(THF)] (Y−N = 2.197(5) Å; Y−N−C = 154.9(4)°).34 The coordination sphere about the six-coordinate yttrium center is completed by an iodide and a THF molecule. The reaction of 1 with the benzopyrone coumarin affords, via ring opening of the α,β-unsaturated cyclic lactone, the ring-opened dinuclear aryloxide−enolate complex [Y2{C(PPh2NSiMe3)2[C(O)(CHCHC6H4O-2)]-κ2-N,O:μ,κ-O′}2(I)(μ-I)(THF)] (7) (Scheme 2) in 15% crystalline yield. In contrast, previously reported reactions of chromium35 and titanium36 carbenes with coumarin have yielded exclusively the corresponding metalloWittig product by reaction at the ketone functionality. 7 is proposed to form by sequential Y−O, C−C, and CC bond formation and cleavage of the C−O ester linkage and the CO and YC double bonds (Scheme 3). Following coordination of coumarin to yttrium through the ketone lone pair, nucleophilic attack of the ketyl carbon by the carbene occurs, which leads to a

Figure 6. Molecular structure of 7·3.25C7H8 with selective atom labeling. Displacement ellipsoids are set at 40% probability, and hydrogen atoms and lattice solvent are omitted for clarity.

Table 1. 7 is dinuclear, and both yttrium centers exhibit distorted-pentagonal-bipyramidal geometries, although they have different ligand environments. The formation of formal C(1)C(32) (1.400(8) Å) and C(45)C(76) (1.386(8) Å) double bonds (idealized bond lengths from sum of covalent radii: C−C, 1.50 Å; CC, 1.34 Å)38 results in only one bis(iminophosphorano) arm of each aryloxide−enolate ligand

Scheme 3. Proposed Mechanism of Formation of 7

1245

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spectrum as a consequence of the two iminophosphorano arms being inequivalent (δ −0.18 and 29.27 ppm, 2JPP = 35.6 Hz). Notable resonances observed in the 13C{1H} NMR spectrum of 8 include the two carbons of the CC double bond, which exhibit the expected multiplicities and couplings to 31P (δ 93.36 ppm, dd, JPC = 112.7 and 89.6 Hz; δ 185.80 ppm, d, 2JPC = 2.8 Hz), although the carbon bound to oxygen only couples to one 31P center and this coupling constant is smaller than that observed for 7. Single crystals of 8·1.5C7H8 were grown, and the structure was determined by X-ray crystallography, which is depicted in Figure 7 with selected bond lengths and angles compiled in

coordinating to Y(1) and Y(2), respectively, with the other N-substituents isolated from the metal coordination environment. The C(32)−O(1) (1.311(7) Å) and C(76)−O(4) (1.309(7) Å) distances are also indicative of some delocalization (idealized bond lengths from sum of covalent radii: C−O, 1.38 Å; CO, 1.24 Å).38 The enolate Y(1)−O(1) (2.158(4) Å) and Y(2)−O(4) (2.146(4) Å) bonds, which are best compared with those found for [Y{N(SiMe 3 )C 6 H 3 Pr i 2 -2,6} 2 (OCHCH2){ClLi(THF)3}] (2.103(7) Å),39 [{Y(Cp*2)}2(μ-OCHCHCC)] (2.213(6) Å),40 and [Y(Cp)2(η2-OC(CPh2-4)(Ph2-7,7)(O-6){3.2.0})] (2.106(2) Å),41 give rise to six-membered Y−N−P−C−C−O metallacycles that exhibit pseudo-chair conformations. The aryloxide groups bridge the two yttrium centers (Y−O range 2.236(4)−2.308(4) Å, 2.278(4) Å mean) and exhibit a mean Y−O distance that is statistically indistinguishable from the mean bridging aryloxide Y−O distance observed for [Y(OC6H3Me2-2,6)2(μ-OC6H3Me22,6)(THF)]2 (2.276(6) Å mean).42 The coordination spheres of Y(1) and Y(2) are supplemented by a THF and a bridging iodide ligand or one bridging and one terminal iodide, respectively. Completing the coordination sphere at each yttrium, the close approach of two methyl groups of the N(SiMe3) substituents leads to two Y···H contacts per yttrium center (range 2.730−3.262 Å), and short Y(1)···C(31) (3.075(8) Å) and Y(2)···C(74) (3.308(8) Å) distances are observed. Comparable agostic-type interactions have previously been reported for group 1 BIPMH complexes.43 Benzoyl fluoride reacts with 1 to afford the bis-enolate complex [Y{C(PPh2NSiMe3)2[C(O)(Ph)]-κ2N,O}2(I)] (8) (Scheme 2) in 13% crystalline yield. This is accompanied by the formation of a white powder that exhibits very low solubility in THF which is consistent with the formal formation of “YF2I(THF)n”. The isolation of 8 is noteworthy, as to the best of our knowledge this is the first report of the reactivity of benzoyl fluoride with an early-metal carbene complex. Since the precoordination of ketones to yttrium prior to further reaction has been demonstrated previously,22 it is postulated that the formation of 8 proceeds initially by coordination of benzoyl fluoride to yttrium through the lone pair of the ketone, followed by nucleophilic attack of the ketyl carbon by the carbene to form a C−C bond and an alkoxide (Scheme 4). This

Figure 7. Molecular structure of 8·1.5C7H8 with selective atom labeling. Displacement ellipsoids are set at 40% probability, and hydrogen atoms and lattice solvent are omitted for clarity.

Table 1. The yttrium center of 8 exhibits an approximately pentagonal-bipyramidal geometry, with N(1) and N(3) occupying the axial sites and O(1), O(2), C(28), C(65), and I(1) taking up the equatorial positions. Four agostic-type C− H···Y interactions (Y···H range 2.763−3.540 Å; Y(1)···C(28) = 3.038(8) Å, Y(1)···C(65) = 3.548(7) Å) from two of the methyl groups of the N-silyl substitutuents are apparent, and these are similar to those observed in 7 (see above). Also in common with 7, the ligand scaffolds of 8 have only one coordinated iminophosphorano arm each and upon coordination form six-membered pseudo-chair metallacycles and exhibit similar Y−O (2.135(5) Å mean), C−O (1.311(3) Å mean) and CC (1.376(7) Å mean) distances. All other metrical parameters in the structure of 8 are unremarkable.

Scheme 4. Proposed Mechanism of Formation of 8

■

SUMMARY AND CONCLUSIONS A reactivity study of the planar T-shaped carbene [Y(BIPM)(I)(THF)2] (1) with unsaturated substrates is reported. 1 has been shown to react with a phosphaalkyne in a head-to-tail fashion to afford [Y{C(PPh2NSiMe3)2(PCBut)-κ4C,C′,N,N′}(I)] (2) by a [2 + 2] cycloaddition reaction. A similar reactivity profile was observed for the reactions between 1 and heteroallenes, which furnished [Y{C(PPh2NSiMe3)2[C(NCy)2]κ4C,N,N′,N″}(I)(THF)] (3) and [Y{C(PPh2NSiMe3)2[C(O)(NBut)]-κ4C,N,N′,O}(I)(THF)2] (4). The reaction of 1 with the heteroallene tert-butyl isothiocyanate does not fit this pattern and instead yields the ketenimine ButNC C(PPh2NSiMe3)2 (5), with the concomitant formal elimination of “YSI(THF)n” by a pseudo-Wittig reaction. An arylamine has been shown to undergo a 1,2-addition reaction across the YC bond of 1, such as in the synthesis of the anilide−methanide

alkoxide then rearranges by cleavage of the Y−Cmethanide linkage and the C−F bond with concomitant formation of a CC double bond and a Y−F bond to give the intermediate complex “[Y{C(PPh2 NSiMe3 ) 2 [C(O)(Ph)]-κ 2N,O}(F)(I)(THF)x]”. Then, rapid rearrangement to 8 and the thermodynamically favored product “YF2I(THF)n” by ligand scrambling occurs. As with 7, 8 exhibits two doublet resonances in the 31P{1H} NMR 1246

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Organometallics

Article

H, 6.62; N, 5.28. 1H NMR (d6-benzene, 298 K): δ 0.26 (s, 18H, Si(CH3)3), 0.46 (m, 2H, CH-2ax NCy), 1.00 (m, 2H, CHax NCy), 1.17 (m, 2H, CHax NCy), 1.40 (m, 4H, OCH2CH2), 1.51 (m, 2H, CHax NCy), 1.67 (m, 4H, CH NCy), 1.79 (d, 2H, CHeq NCy), 2.01 (m, 4H, CHeq NCy), 2.83 (m, 2H, CH-2eq NCy), 3.56 (m, 1H, CH-1ax NCy), 3.81 (m, 4H, OCH2CH2), 4.29 (m 1H, CH-1ax NCy), 6.76 (t, 3JHH = 7.4 Hz, 4H, m-Ph-CH), 6.88 (t, 3JHH = 7.4 Hz, 2H, p-Ph−CH), 7.00 (m, 3JHH = 7.4 Hz, 6H, m- and p-Ph-CH), 7.50 (dd, 3JPH = 11.6 Hz, 3 JHH = 7.2 Hz, 4H, o-Ph-CH), 7.95 (dd, 3JPH = 12.2 Hz, 3JHH = 6.4 Hz, 4H, o-Ph-CH). 13C{1H} NMR (d6-benzene, 298 K): δ 5.94 (Si(CH3)3), 20.71 (dt, JPC = 102.7 Hz, JYC = 2.3 Hz, CP2), 25.21 (OCH2CH2), 25.79 (C-4 NCy), 26.67 (C-3 NCy), 27.04 (C-3 NCy), 34.47 (C-2 NCy), 34.72 (C-2 NCy), 55.86 (C-1 NCy), 57.89 (C-1 NCy), 68.70 (OCH2CH2), 127.25 (vt, 2JPC = 6.1 Hz, o-Ph-CH), 130.37 (p-Ph-CH), 130.66 (p-Ph-CH), 132.65 (vt, 3JPC = 5.0 Hz, m-Ph-CH), 132.93 (vt, 3JPC = 5.0 Hz, m-Ph-CH), 136.78 (dd, JPC = 118.8 Hz, 3JPC = 11.5 Hz, ipso-Ph-C), 153.15 (dd, 2JPC = 6.1 Hz, 3.8 Hz, CN2). 31P{1H} NMR (d6-benzene, 298 K): δ 16.57 (d, 2JYP = 3.2 Hz, CP2). 29Si{1H} NMR (d6-benzene, 298 K): δ −3.90 (SiMe3). FTIR ν/cm−1 (Nujol): 1534 (m), 1245 (m), 1231 (m), 1109 (m), 1069 (m), 1049 (m), 1018 (m), 988 (m), 839 (s, br), 766 (m), 743 (m), 695 (m), 655 (w), 602 (m), 578 (w), 535 (w), 521 (m). Preparation of [Y{C(PPh2NSiMe3)2[C(O)(NBut)]-κ4C,N,N′,O}(I)(THF)2] (4). A solution of ButNCO (0.20 g, 2.00 mmol) in toluene (10 mL) was added dropwise to a precooled (−78 °C) suspension of [Y(BIPM)(I)(THF)2] (1.83 g, 2.00 mmol) in toluene (10 mL). The white slurry was slowly warmed to room temperature with stirring over 24 h. The mixture was filtered, reduced in volume, and stored at −25 °C overnight to afford 4 as colorless crystals. A second crop was obtained. Yield: 1.10 g, 54%. Anal. Calcd for C44H63IN3O3P2Si2Y: C, 52.01; H, 6.25; N, 4.14. Found: C, 51.95; H, 6.18; N, 4.17. 1H NMR (d6-benzene, 298 K): δ 0.49 (s, 18H, Si(CH3)3), 1.15 (s, 9H, C(CH3)3), 1.39 (m, 8H, OCH2CH2), 4.04 (m, 8H, OCH2CH2), 6.65 (vt, 3JHH = 7.2 Hz, 4H, m-Ph-CH), 6.74 (t, 3JHH = 7.2 Hz, 2H, p-Ph-CH), 7.14 (m, 3JHH = 7.4 Hz, 6H, m- and p-Ph-CH), 7.85 (dd, 3 JPH = 12.8 Hz, 3JHH = 6.8 Hz, 4H, o-Ph-CH), 8.29 (dd, 3JPH = 12.8 Hz, JHH = 6.8 Hz, 4H, o-Ph-CH). 13C{1H} NMR (d6-benzene, 298 K): δ 4.17 (Si(CH3)3), 25.10 (OCH2CH2), 30.07 (C(CH3)3), 31.39 (dt, JPC = 111.9 Hz, JYC = 2.3 Hz, CP2), 52.48 (C(CH3)3), 71.09 (OCH2CH2), 127.03 (vt, 2JPC = 6.1 Hz, o-Ph-CH), 127.34 (vt, 2JPC = 6.1 Hz, o-Ph-CH), 130.24 (p-Ph-CH), 130.70 (p-Ph-CH), 133.00 (vt, 3 JPC = 5.3 Hz, m-Ph-CH), 133.07 (dd, JPC = 118.9 Hz, 3JPC = 22.2 Hz, ipso-Ph-C), 134.19 (vt, 3JPC = 5.3 Hz, m-Ph-CH), 134.70 (dd, JPC = 120.4 Hz, 3JPC = 14.6 Hz, ipso-Ph-C), 156.26 (t, 2JPC = 2.8 Hz, NCO). 31 1 P{ H} NMR (d6-benzene, 298 K): δ 20.39 (d, 2JYP = 3.2 Hz, CP2). 29 Si{1H} NMR (d6-benzene, 298 K): δ −3.99 (SiMe3). FTIR ν/cm−1 (Nujol): 1601 (m), 1553 (w), 1348 (w), 1244 (m), 1218 (w), 1166 (w), 1109 (s), 1067 (s), 1038 (s), 836 (s), 772 (m), 741 (m), 693 (m), 661 (m), 607 (m), 543 (w), 519 (m), 508 (m). Preparation of ButNCC(PPh2NSiMe3)2 (5). A solution of ButNCS (0.25 g, 2.20 mmol) in toluene (10 mL) was added dropwise to a precooled (−78 °C) suspension of [Y(BIPM)(I)(THF)2] (1.83 g, 2.00 mmol) in toluene (10 mL). The white slurry was slowly warmed to room temperature with stirring over 24 h. The mixture was filtered, reduced in volume to 2 mL, and stored at 5 °C overnight to afford 5 as colorless crystals. Yield: 0.28 g, 22%. The bulk material was determined to be contaminated with YI3 byproduct. Anal. Calcd for C36H47N3P2Si2·YI3: C, 38.97; H, 4.27; N, 3.79. Found: C, 38.98; H, 4.69; N, 3.17. 1H NMR (d6-benzene, 298 K): δ 0.26 (s, 18H, Si(CH3)3), 0.79 (s, 9H, C(CH3)3), 7.04 (m, 12H, p- and m-Ph-CH), 7.93 (m, 8H, o-Ph-CH). 13C{1H} NMR (d6-benzene, 298 K): δ 4.14 (Si(CH3)3), 29.74 (C(CH3)3), 55.86 (t, JPC = 100.3 Hz, CP2), 59.77 (C(CH3)3), 127.67 (vt, 2JPC = 6.6 Hz, o-Ph-CH), 130.43 (p-Ph-CH), 132.13 (vt, 3JPC = 5.9 Hz, m-Ph-CH), 136.96 (dd, JPC = 107.6 Hz, 3 JPC = 1.5 Hz, ipso-Ph-C), 162.63 (t, 2JPC = 5.9 Hz, ButNCCP2). 31 1 P{ H} NMR (d6-benzene, 298 K): δ −2.58 (CP2). 29Si{1H} NMR (d6-benzene, 298 K): δ −0.69 (SiMe3). FTIR ν/cm−1 (Nujol): 2048 (s, CCN stretch), 1589 (m, br), 1403 (s), 826 (m), 728 (m), 693 (m).

complex [Y(BIPMH)(NHDipp)(I)(THF)] (6). Unusually, the reaction between 1 and coumarin afforded the ring-opened dinuclear aryloxide−enolate complex [Y2{C(PPh2NSiMe3)2[C(O)(CHCHC6H4O-2)]-κ2N,O:μ,κ-O′}2(I)(μ-I)(THF)] (7) instead of the Wittig product that is formed in the reactions of early-transition-metal carbenes with coumarin.35,36 The nonclassical reactivity of yttrium carbenes with carbonyl-functionalized organic substrates has been observed previously22 and highlights how the chemistry of lanthanide carbenes contrasts and complements the chemistry of more established transition-metal carbenes. Finally, benzoyl fluoride has been shown to react with 1 to afford the bis-enolate complex [Y{C(PPh2NSiMe3)2[C(O)(Ph)]-κ2N,O}2(I)] (8) and “YF2I(THF)n” in a novel transformation of benzoyl fluoride mediated by a metal carbene. We are currently investigating the further synthetic utility of lanthanide carbenes with unsaturated organic substrates and will report on these findings in due course.

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EXPERIMENTAL SECTION

General Considerations. All manipulations were carried out using standard Schlenk techniques, or an MBraun UniLab glovebox, under an atmosphere of dry nitrogen. Solvents were dried by passage through activated alumina towers and degassed before use. All solvents were stored over potassium mirrors (with the exception of THF, which was stored over activated 4 Å molecular sieves). Deuterated solvents were distilled from potassium, degassed by three freeze−pump−thaw cycles, and stored under nitrogen. 117 and ButCP24 were prepared according to published procedures. All other chemicals were purchased, and all solid reagents were dried under vacuum for 3 h and all liquid reagents were dried over 4 Å molecular sieves and distilled before use. 1H, 13C, 29 Si, and 31P NMR spectra were recorded on a Bruker 400 spectrometer operating at 400.2, 100.6, 79.5, and 162.0 MHz, respectively; chemical shifts are quoted in ppm and are relative to TMS (1H, 13C, and 29Si) and external 85% H3PO4 (31P). FTIR spectra were recorded on a Bruker Tensor 27 spectrometer. Elemental microanalyses were carried out by Mr. Stephen Boyer at the Microanalysis Service, London Metropolitan University, U.K. or by Dr. Tong Liu at the University of Nottingham. Preparation of [Y{C(PPh2NSiMe3)2(PCBut)-κ4C,C′,N,N′}(I)] (2). A solution of ButCP (0.26 g, 1.00 mmol) in toluene (10 mL) was added dropwise to a precooled (−78 °C) suspension of [Y(BIPM)(I)(THF)2] (0.92 g, 1.00 mmol) in toluene (10 mL). The yellow slurry was slowly warmed to room temperature with stirring over 24 h. The mixture was filtered, reduced in volume to 2 mL, and stored at 5 °C overnight to afford 2 as colorless crystals. Yield: 0.12 g, 14%. Anal. Calcd for C36H47IN2P3Si2Y: C, 49.54; H, 5.43; N, 3.21. Found: C, 49.44; H, 5.46; N, 3.25. 1H NMR (d8-THF, 298 K): δ 0.06 (s, 18H, Si(CH3)3), 0.23 (s, 9H, C(CH3)3), 7.14 (vt, 3JHH = 7.2 Hz, 8H, m-PhCH), 7.24 (m, 3JHH = 7.2 Hz, 4H, p-Ph-CH), 7.42 (m, 8H, o-Ph-CH). 13 C{1H} NMR (d8-THF, 298 K): δ 2.09 (Si(CH3)3), 2.67 (C(CH3)3), 28.81 (d, 2JPC = 6.0 Hz, C(CH3)3), 125.08 (vt, 3JPC = 6.2 Hz, m-PhCH), 125.55 (d, 2JPC = 24.5 Hz, o-Ph-CH), 126.16 (d, 2JPC = 25.3 Hz, o-Ph-CH), 126.94 (p-Ph-CH), 129.03 (vt, 3JPC = 6.2 Hz, m-Ph-CH), 139.95 (vt, JPC = 48.3 Hz, ipso-Ph-C), CP3 and PCBut not observed. 31 1 P{ H} NMR (d8-THF, 298 K): δ −72.23 (br, PCBut), 1.62 (d, 2JPP = 13.0 Hz, CP2). 29Si{1H} NMR (d8-THF, 298 K): δ −2.74 (SiMe3). FTIR ν/cm−1 (Nujol): 1588 (w, br), 1436 (s), 1158 (m), 1113 (s), 1073 (s), 1060 (s), 1039 (s), 935 (m), 840 (s), 769 (m), 752 (m), 739 (m), 712 (m), 693 (m) 655 (m), 622 (m), 607 (m), 553 (m), 510 (m). Preparation of [Y{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N″}(I)(THF)] (3). Toluene (20 mL) was added to a precooled (−78 °C) mixture of [Y(BIPM)(I)(THF)2] (1.83 g, 2.00 mmol) and C(NCy)2 (0.41 g, 2.00 mmol). The white slurry was slowly warmed to room temperature with stirring over 24 h. The mixture was filtered, reduced in volume, and stored at −25 °C overnight to afford 3 as colorless crystals. A second crop was obtained. Yield: 1.14 g, 54%. Anal. Calcd for C48H68IN4OP2Si2Y: C, 54.84; H, 6.53; N, 5.33. Found: C, 54.74; 1247

dx.doi.org/10.1021/om301016j | Organometallics 2013, 32, 1239−1250

Organometallics

Article

Table 2. Crystallographic Data for 2−5 formula fw cryst size, mm cryst syst space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z ρcalcd, g cm−3 μ, mm−1 no. of rflns measd no. of unique rflns, Rint no. of rflns with F2 > 2σ(F2) transmn coeff range R, Rwa (F2 > 2σ(F2)) R, Rwa (all data) Sa no. of params max, min diff map, e Å−3 a

2

3

4

5·0.5C7H8

C36H47IN2P3Si2Y 872.66 0.04 × 0.06 × 0.09 orthorhombic Pnma 20.021(3) 19.555(2) 10.4855(8)

C48H68IN4OP2Si2Y 1050.99 0.03 × 0.06 × 0.06 triclinic P1̅ 11.8218(3) 13.8371(4) 16.3160(4) 92.766(2) 99.723(2) 107.467(2) 2495.39(11) 2 1.399 1.938 8771 8771, 0.083 6659 0.89−0.94 0.0741, 0.1405 0.1103, 0.1569 1.181 533 0.786, −0.722

C44H63IN3O3P2Si2Y 1015.90 0.15 × 0.25 × 0.25 monoclinic P21/n 11.8331(13) 17.3545(18) 23.769(2)

C36H47N3P2Si2·0.5C7H8 685.95 0.02 × 0.12 × 0.18 triclinic P1̅ 14.986(3) 15.291(3) 17.647(4) 90.56(3) 102.89(3) 100.20(3) 3874.6(13) 4 1.176 1.838 30371 13743, 0.0433 10686 0.89−0.99 0.0499, 0.1282 0.0662, 0.1374 1.057 793 0.459, −0.509

4105.1(9) 4 1.412 9.763 9593 3812, 0.1353 2024 0.591−0.760 0.0961, 0.1916 0.1780, 0.2595 1.067 219 1.925, −2.05

102.276(2) 4769.5(8) 4 1.415 2.027 30165 10935, 0.0374 8122 0.6312−0.7508 0.0357, 0.0752 0.0600, 0.0834 1.006 505 1.061, −0.469

Conventional R = ∑||Fo| − |Fc||/∑|Fo|; Rw = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2; S = [∑w(Fo2 − Fc2)2/((no. data) − (no. params))]1/2 for all data. 3.67 (m, 4H, OCH2CH2), 4.92 (dd, 3JHH = 13.2 and 1.6 Hz, 2H, OCCHCHAr), 5.18 (d, 3JHH = 13.2 Hz, 2H, OCCHCHAr), 6.60 (ddd, 3JHH = 7.2 Hz, 4JHH = 1.2 Hz, 2H, Ar-CH), 6.65 (dd, 3JHH = 7.6 Hz, 4JHH = 2.0 Hz, 2H, Ar-CH), 6.69 (br m, 2H, Ar-CH), 6.88 (br m, 4H, Ph-CH), 7.06 (t, 3JHH = 7.6 Hz, 4H, Ph-CH), 7.07 (t, 3JHH = 7.6 Hz, 4H, Ph-CH), 7.14−7.36 (m, 8H, Ar-CH), 7.41 (t, 3JHH = 7.2 Hz, 2H, Ar-CH), 7.50 (br m, 2H, Ar-CH), 7.64 (dd, 3JHH = 5.8 Hz, 4JHH = 3.0 Hz, 4H, Ph-CH), 8.06 (br m, 2H, Ph-CH), 7.64 (ddd, JPH = 14.0 Hz, 3JHH = 7.2 Hz, 4JHH = 2.8 Hz, 4H, o-Ph-CH). 13C{1H} NMR (d8-THF, 298 K): δ 3.39 (Si(CH3)3), 3.42 (Si(CH3)3), 4.57 (Si(CH3)3), 4.61 (Si(CH3)3), 25.43 (OCH2CH2), 67.35 (OCH2CH2), 98.60 (dd, JPC = 119.7 and 91.6 Hz, P2CCO), 116.08 (OCCHCH), 120.84 (OCCHCH), 125.71 (Ar-CH), 126.17 (br, Ar-CH), 126.20 (Ar-CCHCH), 127.06 (Ar-CH), 127.19 (Ar-CH), 127.30 (Ar-CH), 127.41 (Ar-CH), 127.53 (Ar-CH), 127.66 (d, 2JPC = 6.0 Hz, o-Ph-CH), 127.79 (Ar-CH), 129.22 (Ar-CH), 129.48 (d, 3JPC = 2.0 Hz, m-Ph-CH), 130.01 (vt, 3JPC = 3.0 Hz, m-Ph-CH), 130.62 (d, 3JPC = 3.0 Hz, m-PhCH), 131.33 (vt, 3JPC = 5.0 Hz, o-Ph-CH), 131.89 (br, Ar-CH), 132.12 (ipso-Ar-C), 132.31 (Ar-CH), 132.38 (d, 3JPC = 3.0 Hz, m-Ph-CH), 132.49 (Ar-CH), 133.06 (ipso-Ph-C), 133.54 (ipso-Ph-C), 134.08 (d, 2 JPC = 10.0 Hz, o-Ph-CH), 134.31 (d, 2JPC = 12.1 Hz, o-Ph-CH), 134.57 (ipso-Ph-C), 135.41 (ipso-Ph-C), 136.48 (ipso-Ph-C), 139.76 (d, JPC = 6.0 Hz, ipso-Ph-C), 140.67 (d, JPC = 6.0 Hz, ipso-Ph-C), 162.31 (d, 2 JYC = 6.0 Hz, Ar-CO), 184.75 (dd, 2JPC = 13.6 and 3.5 Hz, P2CCO). 31 1 P{ H} NMR (d8-THF, 298 K): δ 4.91 (d, 2JPP = 37.3 Hz, CPNY), 28.32 (d, 2JPP = 37.3 Hz, CPN). 29Si{1H} NMR (d8-THF, 298 K): δ −15.68, −15.40, −1.65 (SiMe3). FTIR ν/cm−1 (Nujol): 1627 (m, CC stretch), 1588 (m), 1565 (m), 1295 (s), 1223 (m), 1106 (s), 1046 (s), 828 (s), 744 (s), 693 (m), 548 (m), 518 (m). Preparation of [Y{C(PPh2NSiMe3)2[C(O)(Ph)]-κ2N,O}2(I)] (8). A solution of PhCOF (0.27 g, 2.20 mmol) in toluene (10 mL) was added dropwise to a precooled (−78 °C) suspension of [Y(BIPM)(I)(THF)2] (1.83 g, 2.00 mmol) in toluene (10 mL). The yellow slurry was slowly warmed to room temperature with stirring over 24 h. The mixture was filtered away from the resulting white powder, reduced in volume to 10 mL, and stored at 5 °C overnight to afford 8 as colorless crystals. Yield: 0.22 g, 13%. Anal. Calcd for C76H86IN4O2P4Si4Y: C, 59.29; H, 5.63; N, 3.64. Found: C, 59.12; H, 5.76; N, 3.55. 1H NMR

Preparation of [Y(BIPMH)(NHDipp)(I)(THF)] (6). NH2Dipp (0.42 mL, 2.20 mmol) was added dropwise via syringe to a precooled (−78 °C) suspension of [Y(BIPM)(I)(THF)2] (1.83 g, 2.00 mmol) in toluene (10 mL). The white slurry was slowly warmed to room temperature with stirring over 24 h. Volatiles were removed in vacuo, and the resulting white solid was recrystallized from THF (12 mL) to afford 6 as colorless crystals. A second crop was obtained. Yield: 1.29 g, 59%. Anal. Calcd for C51H73IN3O2P2Si2Y: C, 55.98; H, 6.73; N, 3.84. Found: C, 55.76; H, 6.57; N, 3.65. 1H NMR (d8-THF, 298 K): δ 0.29 (s, 18H, Si(CH3)3), 0.98 (d, JHH = 5.2 Hz, 12H, CH(CH3)2), 1.26 (br, 1H, HCP2), 1.82 (m, 4H, OCH2CH2), 1.92 (t, 2JPH = 2.6 Hz, 1H, HCP2), 3.18 (m, 2H, CH(CH3)2), 3.67 (m, 4H, OCH2CH2), 4.59 (s, 1H, NHDipp), 6.35 (t, 3JHH = 6.8 Hz, 1H, p-Dipp-CH), 6.75 (d, 3 JHH = 6.8 Hz, 2H, m-Dipp-CH), 7.02 (br, 4H, Ph-CH), 7.23 (br, 4H, Ph-CH), 7.31 (t, 3JHH = 8.0 Hz, 4H, Ph-CH), 7.44 (br, 4H, Ph-CH), 7.50 (d, 3JHH = 6.0 Hz, 4H, Ph-CH), 8.08 (t, 3JHH = 8.0 Hz, 4H, o-Ph-CH). 13C{1H} NMR (d8-THF, 298 K): δ 4.72 (Si(CH3)3), 17.91 (dt, JPC = 87.5 Hz, JYC = 4.5 Hz, HCP2), 23.35 (CH(CH3)2), 25.41 (OCH2CH2), 28.37 (CH(CH3)2), 67.27 (OCH2CH2), 114.22 (p-Dipp-CH), 121.59 (m-Dipp-CH), 127.53 (d, 3JPC = 14.1 Hz, m-Ph-CH), 128.15 (d, 3JPC = 12.1 Hz, m-Ph-CH), 130.13 (p-Ph-CH), 131.16 (p-Ph-CH), 131.62 (d, 2JPC = 11.1 Hz, o-Ph-CH), 132.83 (ipso-Ph-C), 133.68 (ipso-Ph-C), 134.10 (o-Dipp-C), 133.50 (d, JPC = 10.1 Hz, ipso-Ph-C), 136.47 (d, JPC = 9.1 Hz, ipso-Ph-C), 151.99 (d, 2 JYC = 3.0 Hz, ipso-Dipp-C). 31P{1H} NMR (d8-THF, 298 K): δ 19.17 (d, 2JYP = 6.5 Hz, HCP2). 29Si{1H} NMR (d8-THF, 298 K): δ −1.83 (SiMe3). FTIR ν/cm−1 (Nujol): 1587 (w, br), 1404 (m), 929 (w), 831 (m), 693 (m). Preparation of [Y2{C(PPh2NSiMe3)2[C(O)(CHCHC6H4O-2)]κ2N,O:μ,κO′}2(I)(μ-I)(THF)] (7). Toluene (20 mL) was added to a precooled (−78 °C) mixture of [Y(BIPM)(I)(THF)2] (1.83 g, 2.00 mmol) and coumarin (0.29 g, 2.00 mmol). The yellow slurry was slowly warmed to room temperature with stirring over 24 h. The mixture was filtered, reduced in volume to 2 mL, and stored at 5 °C overnight to afford 7 as colorless crystals. Yield: 0.33 g, 15%. Anal. Calcd for C84H96I2N4O5P4Si4Y2: C, 52.83; H, 5.07; N, 2.94. Found: C, 52.71; H, 4.98; N, 2.91. 1H NMR (d8-THF, 298 K): δ −0.31 (s, 18H, Si(CH3)3), 0.09 (s, 18H, Si(CH3)3), 1.81 (m, 4H, OCH2CH2), 1248

dx.doi.org/10.1021/om301016j | Organometallics 2013, 32, 1239−1250

Organometallics

Article

Table 3. Crystallographic Data for 6−8 formula fw cryst size, mm cryst syst space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z ρcalcd, g cm−3 μ, mm−1 no. of rflns measd no. of unique rflns, Rint no. of rflns with F2 > 2σ(F2) transmn coeff range R, Rwa (F2 > 2σ(F2)) R, Rwa (all data) Sa no. of params max, min diff map, e Å−3 a

6·C4H8O

7·3.25C7H8

8·1.5C7H8

C47H65IN3OP2Si2Y·C4H8O 1094.05 0.05 × 0.13 × 0.39 monoclinic P21/c 12.2756(2) 45.6639(7) 9.47291(14)

C84H96I2N4O5P4Si4Y2·3.25C7H8 2208.94 0.05 × 0.10 × 0.15 triclinic P1̅ 14.0687(6) 16.9323(7) 22.4949(9) 96.996(3) 90.722(4) 93.541(4) 5307.5(4) 2 1.382 7.434 37164 18755, 0.042 16371 0.68−0.85 0.0579, 0.165 0.0651, 0.176 1.19 1123 1.57, −2.64

C76H86IN4O2P4Si4Y·1.5C7H8 1677.74 0.02 × 0.04 × 0.17 triclinic P1̅ 12.4201(3) 16.6524(4) 22.1146(3) 83.0555(16) 82.7864(15) 69.759(2) 4242.65(15) 2 1.313 5.447 30022 15187, 0.048 12513 0.93−0.99 0.0479, 0.113 0.0623, 0.120 1.10 905 0.69, −0.92

99.2161(15) 5241.50(14) 4 1.386 7.514 21575 9428, 0.045 8440 0.279−0.717 0.0483, 0.134 0.0582, 0.137 1.23 569 1.21, − 0.93

Conventional R = ∑||Fo| − |Fc||/∑|Fo|; Rw = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2; S = [∑w(Fo2 − Fc2)2/((no. data) − (no. params))]1/2 for all data.

(d6-benzene, 298 K): δ 0.01 (s, 18H, Si(CH3)3), 0.11 (s, 18H, Si(CH3)3), 6.84 (t, 3JHH = 7.2 Hz, 8H, Ph-CH), 6.89 (d, 3JHH = 7.2 Hz, 8H, Ph-CH), 6.91−7.13 (br m, 12H, Ph-CH), 7.22 (br m, 2H, Ph-CH), 7.31 (d, 3JHH = 6.8 Hz, 4H, Ph-CH), 7.35−7.70 (br m, 10H, Ph-CH), 7.89 (br m, 2H, Ph-CH), 8.08 (br m, 2H, Ph-CH), 8.27 (br m, 2H, Ph-CH). 13C{1H} NMR (d6-benzene, 298 K): δ 1.18 (Si(CH3)3), 4.09 (d, JYC = 3.0 Hz, Si(CH3)3), 4.35 (d, JYC = 4.0 Hz, Si(CH3)3), 93.36 (dd, JPC = 112.7 Hz, 89.6 Hz, CP2), 127.14 (Ph-CH), 127.70 (Ph-CH), 127.94 (Ph-CH), 128.33 (Ph-CH), 128.76 (Ph-CH), 129.09 (Ph-CH), 129.32 (br, Ph-CH), 129.55 (Ph-CH), 130.42 (PhCH), 130.64 (Ph-CH), 131.52 (t, 3JPC = 5.0 Hz, m-Ph-CH), 131.94 (br, Ph-CH), 132.42 (Ph-CH), 132.57 (Ph-CH), 132.68 (Ph-CH), 134.35 (br, ipso-Ph-C P), 138.99 (d, JPC = 101.6 Hz, ipso-Ph-C P), 140.72 (ipso-Ph-C), 140.81 (ipso-Ph-C), 185.80 (d, 2JPC = 2.8 Hz, PhCO). 31P{1H} NMR (d6-benzene, 298 K): δ −0.18 (d, 2JPP = 35.6 Hz, CPN), 29.27 (d, 2JPP = 35.6 Hz, CPNY). 29Si{1H} NMR (d6-benzene, 298 K): δ −15.82, −15.51, −3.32 (SiMe3). FTIR ν/cm−1 (Nujol): 1590 (w, br), 1403 (m), 1155 (w), 1105 (m), 742 (m), 691 (m), 539 (w). X-ray Crystallography. Crystal data for compounds 2−8 are given in Tables 2 and 3, and further details of the structure determinations are given in the Supporting Information. Bond lengths and angles are given in Table 1. Crystals were examined variously on a Bruker APEX CCD area detector diffractometer using graphitemonochromated Mo Kα radiation (λ = 0.71073 Å) or on an Oxford Diffraction SuperNova Atlas CCD diffractometer using mirrormonochromated Cu Kα radiation (λ = 1.5418 Å). Intensities were integrated from data recorded on 0.3° (APEX) or 1° (SuperNova) frames by ω rotation. Data for 3 were collected by the National Service on a Bruker-Nonius APEX II diffractometer using confocal mirrormonochromated Mo Kα radiation (λ = 0.71073 Å) with intensities integrated from data recorded on φ and ω scans. Cell parameters were refined from the observed positions of all strong reflections in each data set. Semiempirical absorption correction based on symmetry-equivalent and repeat reflections (APEX) or Gaussian grid face-indexed absorption correction with a beam profile correction (Supernova) were applied. The structures were solved variously by direct and heavy atom methods and were refined by full-matrix least squares on all unique F2 values,

with anisotropic displacement parameters for all non-hydrogen atoms and with constrained riding hydrogen geometries; Uiso(H) was set at 1.2 (1.5 for methyl groups) times Ueq of the parent atom. The largest features in final difference syntheses were close to heavy atoms and were of no chemical significance. Highly disordered solvent molecules of crystallization in 5·0.5C7H8, 7·3.25C7H8, and 8·1.5C7H8 could not be modeled and were treated with the Platon SQUEEZE procedure.44 Programs used were Bruker AXS SMART45 and CrysAlisPro46 (control), Bruker AXS SAINT45 and CrysAlisPro46 (integration), and SHELXTL47 and OLEX248 (structure solution and refinement and molecular graphics).

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ASSOCIATED CONTENT

S Supporting Information *

CIF files giving crystallographic data for 2−8. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Royal Society for a University Research Fellowship (S.T.L.), and the EPSRC, European Research Council, and the University of Nottingham for generously supporting this work. We also thank the EPSRC UK National X-ray Crystallography Service at the University of Southampton49 for the collection of the crystallographic data for 3.

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REFERENCES

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