Transition Metal Complexes of a “Half-Parent” Phosphasilene Adduct

Article pubs.acs.org/Organometallics

Transition Metal Complexes of a “Half-Parent” Phosphasilene Adduct Representing Silylene→Phosphinidene→Metal Complexes Kerstin Hansen,† Tibor Szilvási,‡ Burgert Blom,†,§ and Matthias Driess*,† †

Metalorganics and Inorganic Materials, Department of Chemistry, Technische Universität Berlin, Straße des 17. Juni 135, Sekr. C2, 10623 Berlin, Germany ‡ Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Szent Gellért tér 4, 1111 Budapest, Hungary S Supporting Information *

ABSTRACT: The first [M(CO)5] complexes (M = Cr, Mo, W) bearing a donor-stabilized “half-parent” phosphasilene, in which the lone pair of the phosphorus atom coordinates to a metal center, have been synthesized and fully characterized. The latter complexes 2a (M = Cr), 2b (M = Mo), and 2c (M = W) result from conversion of the “half-parent” phosphasilene-DMAP adduct 1, LSi(dmap)PH (DMAP = 4-N,N-dimethylaminopyridine; L = CH[(CCH2)CMe(NAr)2]; Ar = 2,6-iPr2C6H3), with [M(CO)5thf] in 65− 72% yields. The somewhat unexpected reactivity of LSi(dmap)(H)P:→ W(CO)5 2c toward the strong Lewis acid tris(pentafluorophenyl)borane was investigated. Strikingly, the borane does not abstract the DMAP donor. Most notable, the NMR spectroscopic and structural features of 2a−c, in accord with results by density functional theory calculations, clearly indicate that the already low SiP π-bond character in 1 is almost quenched through coordination of the [M(CO)5] group, suggesting that 2a−c rather represent push−pull donor→silylene→ phosphinidene→metal [DMAP→Si(L):→P(H):→M(CO)5] than SiP→M complexes.

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toward the transition metal occurs (Scheme 1).24 Inoue et al. have reported a phosphasilene-platinum complex (C) as an

INTRODUCTION Phosphasilenes, compounds bearing a silicon−phosphorus double bond, have attracted the attention of researchers in the last decades due to their versatile reactivity.1,2 Since the NMR spectroscopic evidence of the first phosphasilene in 1984 reported by Bickelhaupt et al.3 and the isolation of the first structurally characterized phosphasilene by Niecke et al. in 1993,4 several other compounds with a SiP bond have been isolated and reported. The SiP functional group bearing a three-coordinate silicon and two-coordinate phosphorus center is polar due to the higher electronegativity of phosphorus vs silicon. Nevertheless, the polar and thus highly reactive SiP bond can be stabilized by taking advantage of donor−acceptor stabilization and/or steric congestion through the presence of bulky substituents on phosphorus or silicon.5−20,2 To date, there exist only scant examples of phosphasilene transition metal complexes: either by coordination of the lone pair on the phosphorus atom to the transition metal or alternatively Pmetalated phosphasilenes. The first example of the latter was synthesized in our group in 1997: the P-ferrio-substituted phosphasilene R2SiP[Fe(CO)2(η5-C5H5)] (R = 2,4,6iPr3C6H2).21 Two further examples, where the hydrogen atom of the “half-parent” phosphasilene (tBu3Si)(iPr3C6H2)SiPH have been substituted with methylzinc22 and a plumbylene β-diketiminate complex fragment,23 respectively, were also reported from our group. Matsuo, Tamao, and coworkers isolated a series of neutral (A) and cationic (B) gold(I) complexes incorporating π-conjugated phosphasilene ligands, where an η1-coordination of the lone pair on the phosphorus © XXXX American Chemical Society

Scheme 1. Some Examples of Coordination of the Lone Pair on Phosphorus to Transition Metals

intermediate, which is stable only at low temperatures and reacts further to a dinuclear platinum complex.25 Recently, Inoue et al. also reported a phosphasilene pentacarbonyl tungsten complex D, where an E/Z isomerization occurs at room temperature.26 “Half-parent” phosphasilene complexes of the type LSi(H)P:→MLn (M = transition metal, Ln = ligand sphere) have, however, eluded isolation, most likely due to the high reactivity of such systems. Received: September 9, 2015

A

DOI: 10.1021/acs.organomet.5b00772 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

material 1. The expected low-field shift of the 31P{1H} resonance signals can be explained by the coordination of the lone pair on the phosphorus atom to the transition metal centers, which results in reduced electron density on the phosphorus atom. The 1H NMR spectra of complexes 2a−c reveal a doublet for the PH moiety, which is shifted to lower field, also indicating that the electron density of the PH moiety is reduced in the complexes compared to 1. This phenomenon can also be confirmed by the increasing 1J(P,H) coupling constants, which are typical for complexes where the phosphorus binds to a σacceptor such as a transition metal.30 In contrast, the 29Si{1H} NMR spectra revealed signals between δ = 1.5 and −3.8 ppm, which are shifted to higher field in comparison to 1. The 1 J(Si,P) coupling constant of the transition metal complexes strongly decreased to 104.1 (2a), 98.8 (2b), and 86.9 (2c) Hz, respectively, indicating substantially reduced Si−P double-bond character in these complexes on coordination. The 1J(Si,P) coupling constant of 2c is even lower than the corresponding value for D (E-isomer: 1J(Si,P) = 106 Hz).26 Crystals of 2a−c suitable for single-crystal XRD analysis were grown in toluene solutions at −30 °C. Figure 1 shows the

Recently, we reported the synthesis of the DMAP-stabilized zwitterionic “half-parent” phosphasilene 1, which bears a highly polarized SiP bond (Scheme 2).27 The NBO analysis of 1 Scheme 2. Synthesis of Compounds 2a−c

suggests enhanced phosphinidene−silylene character 1′ (Scheme 2). In line with that, we showed that the corresponding donor-free “half-parent” phosphasilene LSi PH (L = CH[(CCH2)CMe(NAr)2]; Ar = 2,6-iPr2C6H3)28 is capable of acting as a transfer agent of the parent phosphinidene (:PH) to unsaturated organic substrates (bulky NHC).29 In our continued exploration of the rather rich chemistry of 1, we decided to explore its propensity to act as a ligand toward transition metals. Herein we report the first pentacarbonyl group 6 metal complexes of the donor-stabilized “half-parent” phosphasilene 1, which represent unprecedented push−pull zwitterionic donor→silylene→phosphinidene→metal adducts rather than SiP→metal complexes.

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RESULTS AND DISCUSSION Treatment of 1 with in situ generated M(CO)5thf (M = Cr, Mo, W), which was freshly prepared by UV irradiation of M(CO)6 in THF for 3 h, at low temperatures in THF, afforded the desired complexes 2a−c selectively and in good isolated yields (Scheme 2). They were isolated as bright yellow solids and characterized by multinuclear NMR spectroscopy, high-resolution mass spectrometry (HR-MS), IR spectroscopy, and single-crystal X-ray diffraction (XRD) analysis. Strikingly, the DMAP in 1 does not act as a leaving group27 to form a DMAP-M(CO)5 adduct. The full conversion of 1 to 2a−c could be monitored by 31P NMR spectroscopy. As shown in Table 1, the 31P{1H} resonance signals of the complexes are shifted between Δδ = 7.5 and 43 ppm to lower field, compared to the starting

Figure 1. ORTEP representation of the molecular structure of 2a. Thermal ellipsoids show 50% probability; hydrogen atoms are omitted for clarity, except that at P1. Selected distances (pm) and angles (deg) of 2a: Si1−P1, 218.11(11); Si1−N1, 173.9(2); Si1−N2, 173.9(3); Si1−N3, 184.8(3); P1−Cr1, 251.95(10) N1−Si1−N2, 103.84(12); Si1−P1−Cr1, 128.90(4); P1−Cr1−C39 171.95(12).

molecular structure of the chromium complex 2a (the molecular structures of 2b and 2c are isostructural and can be found in the Supporting Information). The silicon atom in these three transition metal complexes adopts a distortedtetrahedral coordination geometry. The Si−P distances in 2a−c (Table 2) are approximately 4 pm longer than in 1. The P−M bond distances of 251.95(10) in 2a, 267.48(18) in 2b, and

Table 1. Selected NMR Data of 1, 2a−c, and 3 NMR data 1

H (PH) [δ in ppm] 31 P [δ in ppm] 1 J(P,H) [Hz] 29 Si{1H} [δ in ppm] 1 J(Si,P) [Hz] 1 183 J( W,P) [Hz] a

1a

2aa

2bb

2ca

−2.62

−1.55

−1.34

−0.84

−331.7 144.1 8.4

−288.7 190.8 1.5

−312.7 192.9 −2.7

−324.2 198.2 −3.8

−316.5 203.4 0.4

131.8

104.1

98.8

86.9 103.2

124.0 108.1

b

3a b

Table 2. Selected Bond Lengths and Angles of 2a−c Compared to 1

−0.91

Si1−P1 [pm] P1−M [pm] Si1−N3 [pm] Si1−P1−M [deg] P1−M−C39 [deg]

THF-d8, 25 °C. bTol-d8, 25 °C. B

1

2a

2b

2c

212.05(1)

218.11(11) 251.95(10) 184.8(3) 128.90(4)

217.8(2) 267.48(18) 186.1(5) 127.31(8)

218.0(2) 265.53(16) 186.0(6) 127.01(9)

171.95(12)

168.6(2)

168.8(2)

188.07(1)

DOI: 10.1021/acs.organomet.5b00772 Organometallics XXXX, XXX, XXX−XXX

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Organometallics 265.53(16) pm in 2c are similar to those in (SiMe3)3P− M(CO)5,31 respectively. The Si−N3 bond lengths are slightly shorter than those in 1, indicating a stronger interaction between DMAP and the Si center. The IR spectra of 2a−c display one weak band at ν = 2248 cm−1 (2a), ν = 2262 cm−1 (2b), and ν = 2261 cm−1 (2c), respectively, corresponding to the stretching vibration of the PH group. The stretching vibrations of the carbonyl groups are located in the typical region between ν = 1847 and 2061 cm−1. In the solid state, these bands overlap and cannot readily be assigned. However, the IR spectra of toluene solutions of 2a−c reveal five different bands, indicating loss of the local C4v symmetry of the M(CO)5 moiety (Figure 2), similar to

Figure 3. HOMO (left, −4.09 eV) and HOMO−4 (right, −4.78 eV) of complex 2a (see the SI for 2b,c).

phosphorus−metal dative bond is 0.68 (2a, 2c) and 0.67 (2b), respectively, although minor hyperconjugation is present in the case of the HOMO between the nonbonding lone pair of phosphinidene and a d-type orbital. We also calculated the bond dissociation energy (BDE) of the Si−P bond in 1, 2c, and model compound H2SiPH. The BDE of the double bond in H2SiPH is 75.0 kcal·mol−1, while 1, with considerable donor−acceptor character, shows a much smaller BDE, 53.1 kcal·mol−1. Tungsten coordination in 2c further reduces the BDE to 38.9 kcal·mol−1, which also emphasizes the increased donor−acceptor character. Overall, the complete analysis suggests that 2a−c represent rather push−pull donor→ silylene→phosphinidene→metal adducts than SiP→metal complexes. The reactivity and stability of these metal complexes were probed using 2c, which was allowed to react with the strongly Lewis acidic tris(pentafluorophenyl)borane. Interestingly, the borane does not abstract the DMAP, the W(CO)5 group, or the H atom of the PH moiety. The related silylene LSi: reacts with B(C6F5)3 to form the zwitterionic silylene-borane adduct (C6F5)3B-LSi:, where the borane attacks the methylene group at the backbone of the C3N2Si ring.36 The new complex 3 is a brown oil, which hampered purification and crystallization. It was nevertheless characterized by 1H, 11B, 29Si, and 31P NMR spectroscopy (Table 1). Due to the fragility of the compound, the molecular ion could not be observed in the mass spectrum even under soft ionization conditions. The 1H NMR spectrum reveals that the methylene group in the backbone of the ligand is protonated. Additionally, the signal for the γ-CH proton of the C3N2Si ring at δ = 6.53 ppm is shifted 1 ppm to lower field, similar to (C6F5)3B-LSi: (δ = 6.79 ppm), thus indicative of the presence of an aromatic 6π-electron system. The 31P{1H} NMR spectrum reveals a sharp signal at δ = −316.5 ppm, which is shifted 7.7 ppm to lower field compared to 2c, with two pairs of satellite signals. The “larger” satellites correspond to 183W−P couplings (1J(P,W) = 108.1 Hz), whereas the “smaller” ones correspond to that of 29Si with a coupling constant of 1J(P,Si) = 124.0 Hz. The latter coupling constant could also be observed in the 29Si{1H} NMR spectrum, where a doublet appears at δ = 0.4 ppm. The increased 1J(Si,P) coupling constant of 124.0 Hz in 3, compared to 2c (1J(P,Si) = 86.9 Hz), indicates a slight increase of the Si−P double-bond character. DFT calculations support these findings: the WBI in (C6F5)3B-LSi(dmap)(H)P:→W(CO)5 is increased slightly by 0.06 to 1.23, compared to 2c. The NBO charge of the phosphorus atom is also increased from −0.31 in 2c to −0.29 in (C6F5)3B-LSi(dmap)(H)P:→ W(CO)5, which is in accordance with the observed low-field shift in the 31P NMR spectra (see Table S14 in the SI).

Figure 2. Comparative IR spectra of complexes 2a−c in toluene in the range 2150−1750 cm−1.

P(tBu)3W(CO)5.32 This reduced symmetry can also be observed in the molecular structures of 2a−c, where the P1− M−C39 bond angles are between 168.6(2)° and 171.95(12)° (Table 2). In addtion, the C−M−C bond angles in the M(CO)5 moieties of 2a−c differ from 90° or 180°, respectively (see Tables S2, S4, and S6 in the Supporting Information). However, in the 13C NMR spectra of 2a−c only one signal is observed for the CO. To elucidate the bonding situation in the metal complexes 2a−c, density functional theory (DFT) calculations at the B97D/6-31G(d)[M:cc-pVTZ(-PP)] level of theory were performed, which previously proved that it yielded reliable results for the electronic structure of main-group element compounds.33−35 Essentially the three complexes show very similar results: The Wiberg bond indices (WBI) of the SiP bond of 2a−c are 1.17 (2a), 1.18 (2b), and 1.17 (2c), respectively; that is, they are 0.27−0.28 lower than the WBI of 1 (1.44), in accord with the increased bond length observed in the XRD. We have previously shown experimentally28 that it is possible to transfer the phosphinidene (:PH) moiety from LSiPH (L = CH[(CCH2)CMe(NAr)2]; Ar = 2,6-iPr2C6H3) (WBI = 1.68) to an NHC, indicating the importance of the donor− acceptor picture in LSiPH. Compared to this, the reduced WBIs (1.17−1.18) in 2a−c are strong indications for the increased relevance of the donor−acceptor description. The WBI, which is larger than unity, still suggests the minor role of the double-bond resonance structure (Scheme 2), though we note that it can be a consequence of strong hyperconjugation, as HOMO−4 shows (Figure 3). Natural bond orbital (NBO) analysis of 1 and 2a−c indicates the same, as only a σ-type bond is present between the Si and P atoms and two lone pairs at the phosphinidene-like P atom. The WBI of the C

DOI: 10.1021/acs.organomet.5b00772 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

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MS: m/z = 650.30158 [M − (CO)5)]+, calcd 650.30202; 791.28392 [M + H]+, calcd 791.28442. Synthesis of 2b. A solution of [Mo(CO)5·thf], freshly prepared by irradiation of a solution of Mo(CO)6 (23.4 mg, 0.089 mmol) in 3 mL of tetrahydrofuran for 3 h, at −60 °C was added via a Teflon cannula to a stirred solution of 1 (49.2 mg, 0.082 mmol) in 10 mL of tetrahydrofuran at −60 °C. The resulting yellow solution was warmed to room temperature over 2 h and stirred for a further 2 h. All volatiles were removed in vacuo, and the residue was washed three times with nhexane (10 mL). The obtained yellow residue was extracted three times with toluene (20 mL), and the filtrate was concentrated to 4 mL and left at −30 °C for 3 days to the afford a yellow crystalline product, which was separated from the mother liquor by filtration and dried in vacuo for 30 min. Yield: 44.5 mg (65%). 1H NMR (200.13 MHz, Told8, 25 °C): δ [ppm] = −1.34 (d, 1J(P,H) = 192.9 Hz, 1 H, PH), 0.60, 0.86, 0.92, 1.16, 1.31, 1.41, 1.67, 1.75 (each d, 3J(H,H) = 6.9 Hz, 3 H, CHMe2), 1.50 (s, 3 H, NCMe), 1.96 (s, 6 H, NMe2), 2.33, 2.59, 4.02, 4.02 (each sept, 3J(H,H) = 6.9 Hz, 1 H, CHMe2), 3.41 (s, 1 H, NCCHH′), 4.02 (s, 1 H, NCCHH′), 5.45 (s, 1 H, γ-CH), 5.64 (br, 1 H, DMAP), 6.20 (br, 1 H, DMAP), 6.81−7.39 (m, 6 H, 2 × 2,6iPr2C6H3), 8.78 (br, 1 H, DMAP), 9.90 (br, 1 H, DMAP). 13C NMR (100.61 MHz, C6D6, 25 °C): δ [ppm] = 21.4 (NCMe); 24.2, 24.5, 24.5, 25.1, 25.5, 26.0, 26.2, 26.7 (CHMe2); 28.5, 29.1, 29.5, 29.6 (CHMe2); 38.5 (NMe2), 88.6 (NCCH2); 105.7 (γ-C); 124.0, 125.0, 125.3, 125.6, 126.2, 128.4, 128.6, 129.0, 129.3, 136.5, 138,0, 143.4, 146.8, 147.3, 148.0, 148.3, 149.4, 156.2 (NC, 2,6 iPr2C6H3, DMAP), 207.9 (CO). 29Si{1H} NMR (39.76 MHz, Tol-d8, 25 °C): δ [ppm] = −2.7 (d, 1J(Si,P) = 94.8 Hz). 31P{1H} NMR (81.01 MHz, Tol-d8, 25 °C): δ [ppm] = −312.7 (s, 1J(Si,P) = 94.8 Hz). 31P NMR (81.01 MHz, Tol-d8, 25 °C): δ [ppm] = −312.7 (d, 1J(P,H) = 192.9 Hz). IR (KBr): ν[cm−1] = 3061 (w), 2968 (m), 2928 (w), 2868 (w), 2262 (w, P−H), 2060 (m), 1978 (m), 1930 (s), 1908 (s), 1884 (m), 1974 (m), 1851 (s), 1634 (m), 1563 (w), 1466 (w), 1442 (w), 1400 (w), 1380 (w), 1349 (m), 1305 (w), 1231 (w), 1191 (w), 1058 (m), 1025 (m), 917 (w), 804 (w), 612 (w), 594 (w), 541 (w). IR (toluene): ν[cm−1] = 2061 (m), 1978 (w), 1934 (s), 1916 (s), 1888 (m). APCI-MS: m/z = 599.36829 [M − Mo(CO)5 + H]+, calcd 599.36934; 627.19221 [M − DMAP − (CO)2 − PH + H]+, calcd 627.19350; 749.27630 [M − Mo(CO)2 − PH + H]+, calcd 749.27790. Synthesis of 2c. A solution of [W(CO)5·thf], freshly prepared by irradiation of a solution of W(CO)6 (137.2 mg, 0.389 mmol) in 5 mL of tetrahydrofuran for 3 h, at −60 °C was added via a Teflon cannula to a stirred solution of 1 (225 mg, 0.376 mmol) in 20 mL of tetrahydrofuran at −60 °C. The resulting yellow solution was warmed to room temperature over 2 h and stirred for a further 2 h. All volatiles were removed in vacuo, and the residue was washed three times with nhexane (10 mL). The obtained yellow residue was extracted three times with toluene (50 mL), and the filtrate was concentrated to 10 mL and left at −30 °C for 3 days to afford a yellow crystalline product, which was separated from the mother liquor by filtration and dried in vacuo for 30 min. Yield: 249.8 mg (72%). 1H NMR (200.13 MHz, Told8, 25 °C): δ [ppm] = −0.84 (d, 1J(P,H) = 198.2 Hz, 1 H, PH), 0.61, 0.88, 0.98, 1.16, 1.31, 1.41, 1.66, 1.76 (each d, 3J(H,H) = 6.9 Hz, 3 H, CHMe2), 1.49 (s, 3 H, NCMe), 1.98 (s, 6 H, NMe2), 2.33, 2.60, 4.03, 4.03 (each sept, 3J(H,H) = 6.9 Hz, 1 H, CHMe2), 3.41 (s, 1 H, NCCHH′), 4.03 (s, 1 H, NCCHH′), 5.45 (s, 1 H, γ-CH), 5.71 (br, 1 H, DMAP), 7.04 (br, 1 H, DMAP), 6.82−7.39 (m, 6 H, 2 × 2,6-iPr2C6H3), 8.81 (br, 1 H, DMAP), 9.67 (br, 1 H, DMAP). 13C{1H} NMR (100.61 MHz, THF-d8, 25 °C): δ [ppm] = 22.9 (NCMe); 24.0, 24.7, 25.4, 25.6, 25.8, 26.1, 26.4, 27.0 (CHMe2); 29.0, 29.0, 29.5, 29.9 (CHMe2); 39.9 (NMe2), 88.2 (NCCH2); 106.3 (γ-C); 124.5, 125.4, 125.5, 126.3, 128.4, 128.5, 128.9, 137.0, 138.8, 143.1, 148.0, 148.4, 148.4, 148.6, 149.8, 155.4, 158.0 (NC, 2,6-iPr2C6H3, DMAP), 220.0 (CO). 29Si{1H} NMR (39.76 MHz, THF-d8, 25 °C): δ [ppm] = −3.8 (d, 1J(Si,P) = 86.9 Hz). 31P{1H} NMR (81.01 MHz, THF-d8, 25 °C): δ [ppm] = −324.2 (s, 1J(Si,P) = 86.9 Hz, 1J(W,P) = 103.2 Hz). 31P NMR (81.01 MHz, THF-d8, 25 °C): δ [ppm] = −324.2 (d, 1J(P,H) = 198.2 Hz, 1J(W,P) = 103.2 Hz). IR (KBr): ν[cm−1] = 3058 (w), 2970 (m), 2930 (w), 2868 (w), 2261 (w, P−H), 2057 (m), 1963(m), 1919 (s), 1876 (m), 1847 (s), 1633 (m), 1567 (w), 1466 (w), 1442 (w),

SUMMARY The syntheses, isolation, and structures of the unprecedented phosphasilene adduct transition metal complexes 2a−c of the type donor→Si(L)P(H):→M(CO)5 (M = transition metal, L = CH[(CCH2)CMe(NAr)2]) have been reported, starting from the DMAP-stabilized phosphasilene DMAP→Si(L) PH 1 and [M(CO)5thf]. Remarkably, the π-bond between Si and P in 2a−c is even weaker than in 1, and they represent push−pull donor→silylene→phosphinidene→metal (resonance forms 2′a−c) rather than SiP→metal complexes. Additionally, the reactivity of 2c was tested using tris(pentafluorophenyl)borane as reagent. Interestingly, the borane does not abstract the DMAP moiety. In compound 3, the marginal Si−P double-bond character is only marginally increased. So far, efforts to abstract the H atom from the PH moiety in these complexes, which could afford the twocoordinate cationic P species [DMAP→LSiP:→M(CO)5]+, were unsuccessful, but further efforts are under way in this direction.37

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EXPERIMENTAL SECTION

General Considerations. All experiments and manipulations were conducted under dry anaerobic nitrogen using standard Schlenk techniques or in an MBraun inert atmosphere drybox containing an atmosphere of purified nitrogen. Solvents were dried by standard methods and freshly distilled prior use. The starting material 1 was prepared according to literature procedures.25 Solution 1H, 13C, 31P, and 29Si NMR spectra were recorded on Bruker AV 400 (1H: 400.13 MHz, 13C: 100.61 MHz; 29Si: 79.49 MHz) or AFM 200 (1H: 200.13 MHz, 13C: 50.32 MHz) spectrometers. The NMR signals are reported relative to the residual solvent peaks (1H, C6D6: 7.16 ppm; 13C, C6D6: 128.0 ppm) or an external standard (31P, 85% H3PO4: 0.0 ppm; 29Si, TMS: 0.0 ppm). Mass spectra were recorded on a Finnigan MAT95S. IR spectra were recorded on a PerkinElmer Spectrum 100 FT-IR. Synthesis of 2a. A solution of [Cr(CO)5·thf], freshly prepared by irradiation of a solution of Cr(CO)6 (21.1 mg, 0.096 mmol) in 3 mL of tetrahydrofuran for 3 h, at −60 °C was added via a Teflon cannula to a stirred solution of 1 (52.2 mg, 0.087 mmol) in 10 mL of tetrahydrofuran at −60 °C. The resulting yellow solution was warmed to room temperature over 2 h and stirred for a further 2 h. All volatiles were removed in vacuo, and the residue was washed three times with nhexane (10 mL). The obtained yellow residue was extracted three times with toluene (20 mL), and the filtrate was concentrated to 4 mL and left at −30 °C for 3 days to the afford a yellow crystalline product, which was separated from the mother liquor by filtration and dried in vacuo for 30 min. Yield: 47.5 mg (69%). 1H NMR (200.13 MHz, Told8, 25 °C): δ [ppm] = −1.55 (d, 1J(P,H) = 190.8 Hz, 1 H, PH), 0.60, 0.87, 0.92, 1.16, 1.31, 1.41, 1.67, 1.77 (each d, 3J(H,H) = 6.9 Hz, 3 H, CHMe2), 1.50 (s, 3 H, NCMe), 1.94 (s, 6 H, NMe2), 2.33, 2.59, 3.99, 3.99 (each sept, 3J(H,H) = 6.9 Hz, 1 H, CHMe2), 3.42 (s, 1 H, NCCHH′), 4.04 (s, 1 H, NCCHH′), 5.45 (s, 1 H, γ-CH), 5.87 (br, 1 H, DMAP), 6.81−7.39 (m, 6 H, 2 × 2,6-iPr2C6H3), 8.95 (br, 1 H, DMAP), 9.44 (br, 1 H, DMAP). 13C NMR (50.32 MHz, THF-d8, 25 °C): δ [ppm] = 22.8 (NCMe); 23.4, 24.3, 24.7, 24.7, 25.1, 25.4, 26.2, 26.9 (CHMe2); 29.0, 29.1, 29.5, 29.9 (CHMe2); 39.9 (NMe2), 88.3 (NCCH2); 106.4 (γ-C); 123.7, 124.6, 125.4, 125.5, 126.1, 128.5, 128.5, 138.7, 143.1, 143.9, 148.1, 148.3, 148.6, 149.8, 158.0 (NC, 2,6 iPr2C6H3, DMAP), 199.8 (CO). 29Si{1H} NMR (39.76 MHz, THF-d8, 25 °C): δ [ppm] = 1.5 (d, 1J(Si,P) = 104.1 Hz). 31P{1H} NMR (81.01 MHz, THF-d8, 25 °C): δ [ppm] = −288.7 (s, 1J(Si,P) = 104.1 Hz). 31P NMR (81.01 MHz, THF-d8, 25 °C): δ [ppm] = −288.7 (d, 1J(P,H) = 190.8 Hz). IR (KBr): ν[cm−1] = 3071 (w), 2968 (m), 2934 (w), 2871 (w), 2248 (w, P−H), 2049 (m), 1971 (m), 1916 (s), 1879 (s), 1871 (s), 1634 (m), 1566 (w), 1466 (w), 1442 (w), 1403 (w), 1382 (w), 1351 (m), 1309 (w), 1232 (w), 1193 (w), 1061 (m), 1027 (m), 919 (w), 806 (w), 676 (w), 661 (m), 611 (w), 540 (w). IR (toluene): ν[cm−1] = 2048 (m), 1968 (w), 1925 (s), 1910 (s), 1888 (m). ESID

DOI: 10.1021/acs.organomet.5b00772 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

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1401(w), 1380 (w), 1350 (m), 1306 (w), 1232 (w), 1192 (w), 1058 (m), 1026 (m), 918 (w), 806 (w), 599 (w). IR (toluene): ν[cm−1] = 2059 (m), 1969 (w), 1924 (s), 1908 (s), 1884 (m). APCI-MS: m/z = 717.22821 [M − DMAP − (CO)4 + H]+, calcd 717.22570. Synthesis of 3. 2c (34.1 mg, 0.037 mmol) and B(C6F5)3 (21.4 mg, 0.042 mmol) were dissolved in 15 mL of toluene at −50 °C. The resulting yellow solution was warmed to room temperature over 2.5 h and stirred for a further 1 h. The solution was concentrated to 5 mL and left at −30 °C for 3 days to afford a brown oil, which was separated from the mother liquor by decantation. 1H NMR (500.25 MHz, THF-d8, 25 °C): δ [ppm] = −0.91 (d, 1J(P,H) = 203.4 Hz, 1 H, PH), 0.71, 1.09, 1.14, 1.57 (each d, 3J(H,H) = 6.9 Hz, 6 H, CHMe2), 2.24 (s, 6 H, NCMe), 2.21, 3.24 (each sept, 3J(H,H) = 6.9 Hz, 2 H, CHMe2), 3.37, 3.38 (s, 3 H, NMe2), 6.53 (s, 1 H, γ-CH), 7.13 (dd, 3 J(H,H) = 7.6 Hz, 2 H, DMAP), 7.30−7.51 (m, 6 H, 2 × 2,6iPr2C6H3), 8.39 (d, 3J(H,H) = 7.5 Hz, 1 H, DMAP), 9.11 (d, 3J(H,H) = 7.5 Hz, 1 H, DMAP). 11B{1H} NMR (160.46 MHz, THF-d8, 25 °C): δ [ppm] = 0.1 (br), 5.5 (br). 29Si{1H} NMR (39.76 MHz, THFd8, 25 °C): δ [ppm] = 0.4 (d, 1J(Si,P) = 124.0 Hz). 31P{1H} NMR (81.01 MHz, THF-d8, 25 °C): δ [ppm] = −316.5 (s, 1J(Si,P) = 124.0 Hz, 1J(W,P) = 108.1 Hz). 31P NMR (81.01 MHz, THF-d8, 25 °C): δ [ppm] = −316.5 (d, 1J(P,H) = 203.4 Hz).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00772. Crystallographic data, 2a (CIF) Crystallographic data, 2b (CIF) Crystallographic data, 2c (CIF) Optimized structure, 1 (XYZ) Optimized structure, 2a (XYZ) Optimized structure, 2b (XYZ) Optimized structure, 2c (XYZ) Optimized structure, 3 (XYZ) Optimized structure, (LSidmap) (XYZ) Optimized structure, PHWCO5 (XYZ) Optimized structure, SiH2PH (XYZ) Optimized structure, SiH2 (XYZ) Optimized structure, PH (XYZ) Optimized structure, 2a-borane (XYZ) Optimized structure, 2b-borane (XYZ) Experimental details, X-ray crystal structure analysis, Cartesian coordinates, NBO analysis, and selected NMR and HR-MS spectra of 2a−c and 3 (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address §

Faculty of Humanities and Sciences, Maastricht University, Lenculenstraat 14, 6211 KR, Maastricht, P.O. Box 616, 6200 MD Maastricht, The Netherlands. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the Deutsche Forschungsgemeinschaft (DR 226/17-2) for financial support. T.S. thanks the support of The New Széchenyi Plan TAMOP-4.2.2/B-10/1-2010-0009.

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REFERENCES

(1) Fischer, R. C.; Power, P. P. Chem. Rev. 2010, 110, 3877. E

DOI: 10.1021/acs.organomet.5b00772 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics (36) Driess, M.; Yao, S.; Brym, M.; van Wüllen, C. Angew. Chem., Int. Ed. 2006, 45, 6730; Angew. Chem. 2006, 118, 6882. (37) We have carried out the reaction of 2c with trityl tetrakis(pentafluorophenyl)borate in the hope of isolating the complex [LSiP:→W(CO)5]+B(C6F5)4− with concomitant HCPh3 formation. This reaction afforded a green oil, which precluded purification. The 31 P NMR spectrum of the major product, however, reveals a doublet of the PH moiety at 316.2 ppm with a coupling constant of 1J(P,H) = 204.2 Hz and other spectral features almost identical to those of 3, which suggest attack of the CPh3 moiety at the backbone of the ligand.

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DOI: 10.1021/acs.organomet.5b00772 Organometallics XXXX, XXX, XXX−XXX