Zirconium-catalyzed imine hydrogenation via a frustrated Lewis pair mechanism

Transcription

1 Zirconium-catalyzed imine hydrogenation via a frustrated Lewis pair mechanism Stephanie R. Flynn, Owen J. Metters, Ian Manners, and Duncan F. Wass* School of Chemistry, University of Bristol, Cantock s Close, Bristol, U.K. duncan.wass@bristol.ac.uk Supporting Information Experimental details General considerations Unless otherwise stated, all manipulations were conducted under an inert nitrogen or argon atmosphere employing standard Schlenk-line and glovebox (M-Braun, O 2 < 0.1 ppm, H 2 O < 0.1 ppm) techniques. All glassware was oven dried (200 C) overnight and allowed to cool under vacuum. Imines PhSO 2 N=CPh, MeN=CPh and BnN=CPh were purchased from Sigma-Aldrich and used as received. [Ph 3 C][B(C 6 F 5 ) 4 ], Me 2 SiCp 2 ZrCl 2 were purchased from Strem and used as received. Substrates tbun=chph (1), 1 tbun=ch(m-omec 6 H 4 ), 2 tbun=ch(m-brc 6 H 4 ), 3 tbun=ch(p- BrC 6 H 4 ), 3 (p-clc 6 H 4 )N=CHPh, 4 tbun=c(me)(ph), 5 tbun=ch(p-nme 2 C 6 H 4 ) 6 and (p- OMeC 6 H 4 )N=CHPh 7 were prepared according to the literature. 2,4,6-Trimethylphenol was purchased from Sigma-Aldrich, dissolved in hexane, dried over CaH 2, filtered and the solvent removed in vacuo and sublimed before use (25 C, 2 x 10-2 mmhg). Complexes [Cp 2 ZrO(C 6 H 4 )P(tBu) 2 ][B(C 6 F 5 ) 4 ] (3), 1 Ind 2 ZrMe 2, 8 (tbuc 5 H 4 ) 2 ZrMe 2, 9 (C 5 Me 5 ) 2 ZrMe 2 and Cp 2 ZrMe 2 were prepared according to the literature. 10 Common laboratory solvents were collected from an Anhydrous Engineering column purification system, 10 subject to 3 cycles of freeze-pump-thaw degassing and stored over 3Å molecular sieves. Aromatic solvents (deuterated and protio) were purchased from Sigma-Aldrich, dried over 4 Å molecular sieves and distilled prior to use. Benzonitrile was dried over 3 Å molecular sieves. A series of hydrogenation experiments were performed in an NMR tube fitted with Teflon needle valve. NMR spectra were recorded at 25 C using a JEOL ECP 300 spectrometer (300 MHz), Varian 400 and 500 spectrometers (400 and 500 MHz respectively) and a Bruker 500 spectrometer with cryo-enhanced probe (500 MHz) and referenced to an internal standard (residual solvent signal for 1 H and 13 C: δ H CDCl ppm, toluene-d , C 6 D , CD 2 Cl , PhCl-d ; δ C CDCl ppm, toluene-d , C 6 D , CD 2 Cl , PhCl-d ; BF 3 OEt 2 for 11 B, 85% H 3 PO 4 for 31 P and FCCl 3 for 19 F). The chemical shifts (δ) were recorded in parts per million (ppm) and NMR abbreviations are of the standard form with singlet (s), doublet (d), triplet (t), quartet (q), quintet (qu), multiplet (m) and broad (br).

2 General procedure for imine hydrogenation reactions In an argon filled glovebox, 0.5 ml of a 0.04 M solution of the cationic zirconium complex in halobenzene solvent was added to an NMR tube fitted with a Teflon needle valve. 0.1 ml of a 2M solution of the imine in PhX (X = Cl, F, Br) was added and an initial 1 H NMR spectrum obtained. The NMR tube was attached to a Schlenk line and subjected to freeze-pump-thaw degassing then backfilled with 1 bar hydrogen at room temperature. The sample was inverted 3 times to ensure sufficient mixing and then allowed to stand for the duration of the reaction. For the kinetic comparison, the reaction was followed by 1 H NMR spectroscopy, with disappearance of the signal assigned to the RN=CHR proton and the appearance of methylene signal used to determine conversion. For the substrate screen, 1 H NMR was taken after 90 minutes to determine conversion. Synthesis of Me 2 Si(C 5 H 4 ) 2 ZrMe 2 Adapted from a literature procedure. 9 Me 2 Si(C 5 H 4 ) 2 ZrCl 2 (244 mg, 0.70 mmol) was suspended in hexane (20 ml) and cooled to -78 C. Methyl lithium (1.6 M in Et 2 O, 0.83 ml, 1.33 mmol) was added dropwise and the reaction warmed to room temperature and stirred for 2 hours. Solvent was removed in vacuo and the residue redissolved in hexane. The resulting solution was filtered through celite, the volume reduced to ~5 ml and cooled to -20 C which resulted in the precipitation of white crystals of the title compound (172 mg, 80%). All recorded data consistent with literature values. 9 1 H NMR (400 MHz, toluene-d 8 ): δ 6.88 (t, 4H, J = 2.2 Hz, Cp), 5.76 (t, 4H, J = 2.2 Hz, Cp), 0.52 (s, 6H, Si(CH 3 ) 2 ), (s, 6H, Zr(CH 3 ) 2 ). General synthesis of neutral complexes of the type [R 2 Zr(Me)(O^P)]: Adapted from a literature procedure. 1 The dimethyl zirconocene (1 equiv.) and 2-(di-tertbutylphosphanyl)phenol (1 equiv.) were weighed into separate vials and dissolved in hexane (1-5 ml). The solutions were combined, including washings of each vial, and the solution left to stir for 2-72 hours. Subsequent filtration and removal of volatiles in vacuo yielded the desired products as sticky solids. For clarity, these neutral compounds when not discussed in the main text are given the numbering convention, for example, 4 where 4 is the related cationic complex. Me 2 Si(C 5 H 4 ) 2 Zr(Me)O(C 6 H 4 )P(tBu) 2 (4 ): 98% yield 1 H NMR (400 MHz, PhCl-d 5 ): δ 7.76 (dt, 1H, J = 7.5, 1.5 Hz, H6), 7.32 (dt, 1H, J = 7.1, 1.2 Hz, H3), 6.96 (dt, 1H, J = 7.7, 1.6 Hz, H4), (m, 2H, Cp), (m, 1H, H5), (m, 4H, Cp), (m, 2H, Cp), 1.36 (d, 18H, 3 J HP = 10.2 Hz, C(CH 3 ) 3 ), 0.73 (s, 3H, SiCH 3 ), 0.60 (s, 3H, SiCH 3 ), 0.52 (s, 3H, ZrCH 3 ) 13 C{ 1 H} NMR (100 MHz, PhCl-d 5 ): δ (d, J = 22.1 Hz, C1), (d, J = 3.5 Hz, C6), (d, J = 0.5 Hz, C3), (d, J = 22.7 Hz, C2), (s, ipso-cpsi), (d, J = 2.2 Hz, C5), (d, J = 2.7 Hz, C4), (s, Cp), (s, Cp), (s, Cp), (s, Cp), (s, Cp), 32.2 (d, 1 J CP = 24.0 Hz, C(CH 3 ) 3 ), 31.8 (s, ZrCH 3 ), 30.8 (d, 2 J CP = 15.9 Hz, C(CH 3 ) 3 ), -4.96, (s, Si(CH 3 ) 2 ). 31 P{ 1 H} NMR (161 MHz, PhCl-d 5 ): δ 9.96 (s). HRMS (ESI+, PhF): m/z ([Me 2 Si(C 5 H 4 ) 2 Zr(Me)O(C 6 H 4 )PH(tBu) 2 ]+ 100%, calcd for C 27 H 40 OPSiZr).

3 (tbuc 5 H 4 ) 2 Zr(Me)O(C 6 H 4 )P(tBu) 2 (5 ): 95% yield 1 H NMR (400 MHz, C 6 D 6 ): δ 7.61 (dt, 1H, J = 7.6, 1.8 Hz, H6), (m, 1H, H3), 6.77 (t, 1H, J = 7.6 Hz, H4), 6.55 (dd, 1H, J = 5.1, 2.6 Hz, H5), (m, 2H, Cp), (m, 2H, Cp), (m, 4H, Cp), 1.25 (d, 18H, 3 J HP = 11.3 Hz, PC(CH 3 ) 3 ), 1.19 (s,18h, CpC(CH 3 ) 3 ), 0.75 (s, 3H, ZrCH 3 ); 13 C{ 1 H} NMR (125 MHz, C 6 D 6 ): δ (d, 2 J CP = 23.7 Hz, C1), (s, ipso-cp(tbu)), (d, 3 J CP = 3.2 Hz, C6), (s, C3), (d, 1 J CP = 25.3 Hz, C2), (d, 4 J CP = 3.4 Hz, C5), (s, C4), 110.8, 110.7, 109.8, (Cp), 32.3 (d, 1 J CP = 24.7 Hz, PC(CH 3 ) 3 ), 30.9 (d, 2 J CP = 16.3 Hz, PC(CH 3 ) 3 ), 29.3 (s, CpC(CH 3 ) 3 ), 26.3 (d, J CP = 6.6 Hz, ZrCH 3 ), 22.9 (s, CpC(CH 3 ) 3 ) 31 P{ 1 H} NMR (161 MHz, C 6 D 6 ): δ (s). Satisfactory elemental analysis could not be obtained; see attached NMR spectra for appraisal of purity. Ind 2 Zr(Me)O(C 6 H 4 )P(tBu) 2 (6 ): 95% yield 1 H NMR (400 MHz, toluene-d 8 ): δ 7.57 (dt, 1H, J = 7.7, 1.8 Hz, H6), 7.28 (dq, 2H, J = 8.4, 1.0 Hz, H 4,7 ), 7.21 (dq, 2H, J = 8.4, 1.0 Hz, H 4,7 ), 7.10 (ddd, 1H, J = 8.1, 7.1, 1.7 Hz, H3), 6.87 (ddd, 2H, J = 8.4, 6.6, 1.2 Hz, H 6,5 ), 6.80 (ddd, 2H, J = 8.4, 6.6, 1.2 Hz, H 6,5 ), 6.76 (dt, 1H, J = 7.4, 1.3 Hz, H4), 6.33 (ddd, 1H, J = 8.1, 5.0, 1.3 Hz, H5), 6.06 (ddd, 2H, J = 3.2, 2.1, 0.9 Hz, H 1,3 ), 5.96 (t, 2H, J = 3.3 Hz, H 2 ), 5.73 (ddd, 2H, J = 3.2, 2.1, 0.9 Hz, H 1,3 ), 1.20 (d, 18H, 3 J H,P = 11.4 Hz, C(CH 3 ) 3 ), -0.1 (s, 3H, ZrCH 3 ) 13 C{ 1 H} NMR (125 MHz, toluene-d 8 ): δ (d, J = 23.9 Hz, C1), (d, J = 7.1, C6), (s, C3), (d, J = 22.7 Hz, C2), (s, C 3a,7a ), (s, C 3a,7a ), (s, C 5,6 ), (m, C 4,7 ), (s, C 5,6 ), (d, J = 3.3 Hz, C5), (s, C4), (d, J = 1.9 Hz, C 2 ), (d, J = 1.2 Hz, C 1,3 ), 98.9 (d, J = 1.3 Hz, C 1,3 ), 32.8 (d, J CP = 7.5 Hz, ZrCH 3 ), 32.4 (d, 1 J CP = 24.9 Hz, C(CH 3 ) 3 ), 31.0 (d, 2 J CP = 15.7 Hz, C(CH 3 ) 3 ). 31 P{ 1 H} NMR (161 MHz, toluene-d 8 ): δ (s). Anal. Calcd for C 33 H 39 OPZr: C, 69.07; H, Found: C, 68.92; H, General synthesis of neutral complexes of the type [R 2 Zr(Me)(OMes)]: Synthesised by a modified literature procedure. 7 In a glovebox, stoichiometric amounts of the relevant dimethyl zirconocene and 2,4,6-trimethylphenol were weighed in to separate vials, dissolved in hexane and combined. Gas evolution was evident and the resulting solution stirred for 1 hour. Subsequent removal of solvent in vacuo gave the neutral complexes, which can be recrystallized from hexane at -78 C. Cp 2 Zr(Me)OMes (7): 78% yield. 1 H NMR (300 MHz, CD 2 Cl 2 ): δ 6.73 (s, 2H, Ar-H), 6.09 (s, 10H, Cp), 2.19 (s, 3H, p-ch 3 ), 2.01 (s, 6H, o-ch 3 ), 0.31 (s, 3H, ZrCH 3 ). All recorded data consistent with literature 7

4 Ind 2 Zr(Me)OMes (11 ): 82% yield 1 H NMR (300 MHz, C 6 D 6 ): δ 7.25 (dd, 2H, J = 8.50, 0.93 Hz, H 5,6 ), 7.20 (dd, 2H, J = 8.50, 0.89 Hz, H 5,6 ), 6.84 (m, 2H, H 4,7 ), 6.76 (s, 2H, Ar-H), 6.72 (m, 2H, H 7,4 ), 6.00 (m, 2H, H 1,3 ), 5.68 (m, 2H, H 1,3 ), 5.53 (t, 2H, J = 3.37 Hz, H 2 ), 2.23 (s, 3H, p-ch 3 ), 1.96 (s, 6H, o-ch 3 ), 0.08 (s, 3H, ZrCH 3 ) 13 C NMR (125 MHz, C 6 D 6 ): δ (s, i-c), (s, p-c), (s, m-c), (s, o-c), (s, C 3a,7a ), (s, C 3a,7a ), (s, C 7,4 ), (s, C 7,4 ), (s, C 5,6 ), (s, C 5,6 ), (s, C 2 ), 100.6, 99.1 (s, C 1,3 ), 28.2 (s, ZrCH 3 ), 20.8 (s, p-ch 3 ), 17.8 (s, o-ch 3 ) Satisfactory elemental analysis could not be obtained; see attached NMR spectra for appraisal of purity. Me 2 Si(C 5 H 4 ) 2 Zr(Me)OMes (9 ): 70% yield 1 H NMR (300 MHz, C 6 D 6 ): δ 6.84 (s, 2H, Ar-H), 6.56 (m, 2H, Cp), 6.17 (m, 2H, Cp), 6.10 (m, 2H, Cp), 5.75 (m, 2H, Cp), 2.30 (s, 3H, p-ch 3 ), 2.20 (s, 6H, o-ch 3 ), 0.59 (s, 3H, SiCH 3 ), 0.54 (s, 3H, ZrCH 3 ), 0.40 (s, 3H, Si-CH 3 ) 13 C NMR (125 MHz, C 6 D 6 ): δ (s, i-c), (s, o-c), (s, m-c), (s, p-c), (s, Cp), (s, Cp), (s, Cp), (s, Cp-Si), (s, Cp), 24.0 (s, ZrCH 3 ), -4.5, -6.1 (s, SiCH 3 ) Anal. Calcd for C 22 H 28 OSiZr: C, 61.77; H, Found: C, 61.92; H, (tbuc 5 H 4 ) 2 Zr(Me)OMes (10 ): 75% yield 1 H NMR (300 MHz, C 6 D 6 ): δ 6.75 (s, 2H, Ar-H), 5.94 (m, 2H, Cp), 5.89 (m, 2H, Cp), 5.70 (m, 2H, Cp), 5.42 (m, 2H, Cp), 2.15 (s, 3H, p-ch 3 ), 2.10 (s, 6H, o-ch 3 ), 1.11 (s, 18H, CpC(CH 3 ) 3 ), 0.59 (s, 3H, ZrCH 3 ) 13 C NMR (125 MHz, C 6 D 6 ): δ (s, ipso-c), (s, m-c), (s, p-c), (s, o-c), (s, ipso-cp(tbu)), 112.5, 110.7, 109.0, (s, Cp), (s, C(CH 3 ) 3 ), 31.1 (s, C(CH 3 ) 3 ), 23.3 (s, ZrCH 3 ), 20.3 (s, p-ch 3 ), 17.8 (s, o-ch 3 ) Satisfactory elemental analysis could not be obtained; see attached NMR spectra for appraisal of purity. General synthesis of cationic complexes of the type [R 2 Zr(O^P)][B(C 6 F 5 ) 4 ]: In a glovebox, stoichiometric amounts of the relevant neutral complex [R 2 Zr(Me)(O P(tBu) 2 )] and [DTBP(H)][B(C 6 F 5 ) 4 ] were weighed into separate vials and dissolved in the minimum amount of PhF (note that PhCl and PhBr can also be used interchangeably). The solution of [DTBP(H)][B(C 6 F 5 ) 4 ] was added dropwise to the vial containing the zirconium complex. Gas evolution was evident and the resulting solution was stirred for 1 hour, yielding bright yellow solutions. Due to inherent instability, the complexes were used in situ to investigate the reactivity towards small molecules [Me 2 Si(C 5 H 4 ) 2 ZrO(C 6 H 4 )P(tBu) 2 ][(B(C 6 F 5 ) 4 ] (4): 1 H NMR (400 MHz, PhCl-d 5 ): δ 7.41 (t, 1H, J = 7.8 Hz, H5), (m, 1H, H4), (m, 1H, H6), 6.93 (br s, 2H, Cp), (m, 1H, H3), 6.28 (br s, 2H, Cp), 6.20 (br s, 2H, Cp), 5.37 (br s, 2H, Cp), 1.12 (d, 18H, 3 J HP = 13.3 Hz, C(CH 3 ) 3 ), 0.82 (br s, 3H, SiCH 3 ), 0.56 (br s, 3H, SiCH 3 ).

5 13 C{ 1 H} (100 MHz, PhCl-d 5 ): δ (d, 2 J CP = 15.4 Hz, C1), (d, 4 J CP = 1.1 Hz, C5), (d, 3 J CP = 1.5 Hz, C4), (br s, Cp), (d, 3 J CP = 4.4 Hz, C6), (d, 1 J CP = 26.7 Hz, C2), (br s, Cp), (br s, Cp), (d, 2 J CP = 6.7 Hz, C3), (br s, Cp), (s, ipso-cpsi), 37.6 (d, 1 J CP = 6.0 Hz, PC(CH 3 ) 3 ), 30.0 (d, 2 J CP = 4.6 Hz, PC(CH 3 ) 3 ), -5.2 (br s, SiCH 3 ), -7.3 (br s, SiCH 3 ). 31 P{ 1 H} NMR (161 MHz, PhCl-d 5 ): δ (s). HRMS (ESI+, PhF): m/z ([Me 2 Si(C 5 H 4 ) 2 ZrO(C 6 H 4 )P(tBu) 2 ]+ 100%, calcd for C 26 H 36 OPSiZr). [(tbuc 5 H 4 ) 2 ZrO(C 6 H 4 )P(tBu) 2 ][(B(C 6 F 5 ) 4 ] (5): 1 H NMR (400 MHz, PhCl-d 5 ): δ 7.13 (dt, 1H, J = 0.9, 7.7, H6), 7.03 (ddd, 1H, J = 1.6, 6.0 Hz, H4), (m, 1H, H5), (m, 2H, Cp), 6.39 (dq, 1H, J = 1.0, 4.5 Hz, H3), (m, 2H, Cp), (m, 4H, Cp), 1.11 (d, 18H, 3 J HP = 14.8 Hz, PC(CH 3 ) 3 ), 0.90 (s, 18H, CpC(CH 3 ) 3 ). 13 C{ 1 H} NMR (125 MHz, PhCl-d 5 ): δ (d, 2 J CP = 15.2 Hz, C1), (s, ipso-cp(tbu)), (d, 4 J CP = 2.8 Hz, C5), (d, 3 J CP = 1.4 Hz, C4), (d, 1 J CP = 21.3 Hz, C2), (s, C6), (d, 2 J CP = 4.8 Hz, C3), 115.7, 113.3, 113.2, (Cp), 37.4 (d, J = 4.9 Hz, PC(CH 3 ) 3 ), 31.7 (s, CpC(CH 3 ) 3 ), 30.3 (d, J = 4.7 Hz, PC(CH 3 ) 3 ), 30.1 (s, CpC(CH 3 ) 3 ) 31 P{ 1 H} NMR (161 MHz, PhCl-d 5 ): δ (s). HRMS (ESI+, PhF): m/z ([5]+ 100%, calcd for C 32 H 48 OPZr). [Ind 2 ZrO(C 6 H 4 )P(tBu) 2 ][(B(C 6 F 5 ) 4 ] (6): 1 H NMR (400 MHz, PhCl-d 5 ): δ (m, 5H, H6 and H 4,7 ), 7.53 (pseudo t, 1H, J = 7.3 Hz, H3), (m, 5H, H 6,5 and H4), (m, 1H, H5), (m, 2H, H 1,3 ), (m, 2H, H 2 ), (m, 2H, H 1,3 ), 1.36 (18H, d, 3 J HP = 14.6 Hz, PC(CH 3 ) 3 ). 13 C{ 1 H} NMR (125 MHz, PhCl-d 5 ): δ (d, 2 J CP = 15.6 Hz, C1), (d, 4 J CP = 4.2 Hz, C5), (d, 3 J CP = 1.2 Hz, C4), (s, C 6,5 ), (s, C 3a,5a ), (s, C 6,5 ), (s, C 3a,5a ), (s, C 4,7 ), s, (s, C 4,7 ), (d, 1 J CP = 27.0 Hz, C2), (d, 3 J CP = 3.4 Hz, C6), (s, C 2 ), (d, 2 J CP = 5.0 Hz, C3), (s, C 1,3 ), (s, C 1,3 ), 37.0 (s, 1 J CP = 7.4 Hz, PC(CH 3 ) 3 ), 29.7 (d, 2 J CP = 4.5 Hz, PC(CH 3 ) 3 ) 31 P{ 1 H} NMR (161 MHz, PhCl-d 5 ): δ 55.9 (s). HRMS (ESI+, PhF): m/z ([6 + MeOH]+ 100%, calcd for C 33 H 40 O 2 PZr). General synthesis of cationic complexes of the type [R 2 Zr(OMes)][B(C 6 F 5 ) 4 ]: In a glovebox, stoichiometric amounts of the neutral complex and [Ph 3 C][B(C 6 F 5 ) 4 ] were weighed in to separate vials, dissolved in fluorobenzene and combined. The reaction was near immediate. Due to inherent instability of the cations when subjected to isolation, the solutions were used in situ for the imine hydrogenation [(Cp 2 ZrOMes][B(C 6 F 5 ) 4 ] (8): 1 H NMR (300 MHz, PhCl-d 5 ): δ 6.76 (s, 2H, Ar-H), 5.49 (s, 10H, Cp), 2.19 (s, 3H, p-ch 3 ), 1.74 (s, 6H, o-ch 3 )

6 13 C NMR (125 MHz, PhCl-d 5 ): δ (s, ipso-c), (s, p-c), (s, m-c), (s, o-c), (s, Cp), 20.5 (s, p-ch 3 ), 17.1 (s, o-ch 3 ) HRMS (ESI+, PhF): m/z ([8]+ 100%, calcd for C 19 H 21 OZr). Anal. Calcd for C 43 H 21 BF 20 OZr: C, 49.87; H, Found: C, 49.67; H, [Me 2 Si(C 5 H 4 ) 2 ZrOMes][B(C 6 F 5 ) 4 ] (9): 1 H NMR (300 MHz, PhCl-d 5 ): δ 6.57 (s, 2H, Ar-H), 5.99, 5.56 (br s, 4H, Cp), 2.01 (s, 3H, p-ch 3 ), 1.78 (s, 6H, o-ch 3 ), 0.36 (br s, 6H, Si(CH 3 ) 2 ) 13 C NMR (125 MHz, PhCl-d 5 ): δ (s, ipso-c), (s, p-c), (s, m-c), (s, Cp), (s, o-c), (s, C-Si) (s, Cp), 20.1 (s, p-ch 3 ), 17.6 (s, o-ch 3 ), -6.6 (s, Si(CH 3 ) 2 ) HRMS (ESI+, PhF): m/z ([9]+ 100%, calcd for C 21 H 25 OSiZr). [(tbuc 5 H 4 ) 2 ZrOMes][B(C 6 F 5 ) 4 ] (10): 1 H NMR (300 MHz, PhCl-d 5 ): δ 6.82 (s, 2H, Ar-H), 6.31, 6.14 (m, 4H, Cp), 2.21 (s, 3H, p-ch 3 ), 1.74 (s, 6H, o-ch 3 ), 1.03 (s, 18H, CpC(CH 3 ) 3 ) 13 C NMR (125 MHz, PhCl-d 5 ): δ (s, ipso-c), (s, ipso-cp(tbu)), (s, p-c), (s, o-c), (s, m-c), 117.4, (s, Cp), 33.5 (s, C(CH 3 ) 3 ), 30.6 (s, C(CH 3 ) 3 ), 20.4 (s, p-ch 3 ), 18.4 (o-ch 3 ) HRMS (ESI+, PhF): m/z ([10]+ 100%, calcd for C 27 H 37 OZr). [Ind 2 ZrOMes][B(C 6 F 5 ) 4 ] (11): 1 H NMR (300 MHz, PhCl-d 5 ): δ 7.28 (m, 4H, H 5,6 ), 7.03 (m, 4H, H 4,7 ), 6.71 (s, 2H, Ar-H), 5.98 (d, 4H, J = 3.46 Hz, H 1,3 ), 5.70 (t, 2H, J = 3.46 Hz, H 2 ), 2.25 (s, 3H, p-ch 3 ), 1.83 (s, 6H, o-ch 3 ) 13 C NMR (125 MHz, PhCl-d 5 ): δ (s, ipso-c), (s, m-c), (s, p-c), (s, C 4,7 ), (s, C 3a,5a ), (s, o-c), (s, C 2 ), (s, C 5,6 ), (s, C 1,3 ), 20.5 (s, p-ch 3 ), 17.8 (s, o- CH 3 ) HRMS (ESI+, PhF): m/z ([11]+ 100%, calcd for C 27 H 25 OZr). [(C 5 Me 5 ) 2 ZrOMes][B(C 6 F 5 ) 4 ] was synthesised via an alternative method due to the sluggish reaction between (C 5 Me 5 ) 2 ZrMe 2 and 2,4,6-trimethylphenol. [CPh 3 ][B(C 6 F 5 ) 4 ] (94 mg, 0.1 mmol) was dissolved in PhCl (1 ml) and added dropwise to a PhCl (1 ml) solution of (C 5 Me 5 ) 2 ZrMe 2 (40 mg, 0.1 mmol). 2,4,6-trimethylphenol (14 mg, 0.1 mmol) in PhCl (1 ml) was added dropwise and effervescence observed, with an accompanying colour change from yellow to deep red. The resulting product was precipitated into a large volume of rapidly stirred hexane (20 ml) and the red solid isolated and washed with pentane (3 x 5 ml), After drying in vacuo [(C 5 Me 5 ) 2 ZrOMes][B(C 6 F 5 ) 4 ] was obtained (100 mg, mmol, 85%) [(C 5 Me 5 ) 2 ZrOMes][B(C 6 F 5 ) 4 ] (12): 1 H NMR (300 MHz, PhCl-d 5 ): δ 6.79 (s, 2H, Ar-H), 2.20 (s, 3H, p-ch 3 ), 1.72 (s, 6H, o-ch 3 ), 1.63 (s, 30H, C 5 (CH 3 ) 5 ) 13 C NMR (125 MHz, PhCl-d 5 ): δ (s, ipso-c), (s, p-c), (s, m-c), (s, o-c), (s, C 5 Me 5 ), 20.6 (s, p-ch 3 ), 18.1 (s, o-ch 3 ), 11.0 (s, C 5 (CH 3 ) 5 )

7 HRMS (ESI+, PhF): m/z ([12-H]+ 100%, calcd for C 29 H 41 OZr). Anal. Calcd for C 53 H 41 BF 20 OZr: C, 54.14; H, Found: C, 54.47; H, Stoichiometric activation of D 2 [(C 5 Me 5 ) 2 ZrOMes] (30 mg, 0.02 mmol) and tbun=chph (4 mg, 0.02 mmol) were mixed in PhCl in a glovebox and transferred to a NMR tube fitted with a Teflon needle valve. The tube was removed from the glovebox and subjected to freeze pump thaw degassing prior to pressurising with 1 bar D 2. 2 H NMR spectra were then collected in situ. 2 H NMR (46 MHz, PhCl): δ 6.07 (s, Zr-D), 8.61 (br s, N-D) Attempted activation of H 2 with complexes 3-6 A sample of [R 2 Zr(O P(tBu) 2 )][B(C 6 F 5 ) 4 ] in PhCl was transferred to a NMR tube fitted with Teflon needle valve in a glovebox. The tube was removed from the glovebox and subjected to freeze pump thaw degassing prior to pressurising with 1 bar H 2. After several weeks at room temperature, there was no evidence of reactivity, with only starting material present by 31 P NMR. Similarly, reactivity was not observed with 48 hours at either -30 C or 80 C. References 1 Arrowsmith, M.; Hill, M. S.; Kociok-Koehn, G. Chem-, Eur. J. 2013, 19, Guimond, N.; Fagnou, K. J. Am. Chem. Soc., 2009, 131, Kloc, K.; Kubicz, E.; Młochowski, J.; Syper, L. Synthesis, 1987, Torregrosa, R.; Pastor, I.M.; Yus, M. Tetrahedron, 2005, 61, Barluenga, J.; Jiménez-Aquino, A.; Aznar, F.; Valdés, C. J. Am. Chem. Soc., 2009, 131, Patent: WO2006/27211 A1, Vatmurge, N. S.; Hazra, B. G.; Pore, V. S.; Shirazi, F.; Chavan, P. S.; Deshpande, M. V. Bioorg. Med. Chem. Lett., 2008, 18, Balboni, D.; Camurati, I.; Ingurio, A. C.; Guidotti, S.; Focante, F.; Resconi, L. J. Organomet. Chem., 2003, 683, Rocchigiana, L.; Bellachioma, G.; Zuccaccia, C.; Macchioni, A. J. Organomet. Chem., 2012, 714, Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics, 1996, 15, 1518.

8 Selected NMR spectra for compounds without satisfactory elemental analysis 13 C NMR Spectrum for 5

9 1 H NMR Spectrum for 5

10 13 C NMR Spectrum for 10

11 1 H NMR Spectrum for 10

12 13 C NMR Spectrum for 11

13 1 H NMR Spectrum for 11