Synthesis of (HMDS)2Alh(Μ-H)Li(THF)3, 1

Synthesis of (HMDS)2AlH(μ-H)Li(THF)3, 1

HMDS(H) (4.2 mL, 20 mmol) in THF (10 mL) was added dropwise to a cooled Schlenk flask containing a THF (10 mL) suspension of LiAlH4 (0.38 g, 10 mmol) at 0 oC. The resulting suspension was heated to 40 oC for three hours, cooled to room temperature, and then stirred at room temperature overnight. Filtering the suspension via a celite cannula generated a colourless solution. THF was removed under vacuum and the residues dissolved in hexane (20 mL). Cooling to -30 oC generated a crop of colourless crystals (yield 3.50 g, 6.1 mmol, 61 %).

Synthesis of (HMDS)2Al(μ-H)2Li(κ4-12-crown-4), 3

12-crown-4 (0.08 mL, 0.5 mmol) was added dropwise to a Schlenk flask containing a hexane (3 mL) solution of (HMDS)2Al(μ-H)2Li(OEt2)2, 2 (0.26 g, 0.5 mmol) giving a white precipitate. The reaction was stirred for 1 h, then toluene (2 mL) was added and the Schlenk flask put in the freezer at -26 oC, which produced colourless crystals (yield 0.20 g, 0.38 mmol, 75 %).

Synthesis of (HMDS)2AlH(μ-H)Li(PMDETA), 4

PMDETA (0.10 mL, 0.5 mmol) was added dropwise to a Schlenk flask containing a hexane (3 mL) solution of (HMDS)2Al(μ-H)2Li(OEt2)2, 2 (0.26 g, 0.5 mmol) which instantly formed a white precipitate. The reaction was stirred for 2 h, then volatiles were removed under vacuum leaving the product as a white solid (yield 0.19 g, 0.36 mmol, 72 %). Colourless crystals suitable for X-ray analysis were grown from a toluene (0.5 mL)/hexane (2 mL) solution at -15oC.

Synthesis of [(HMDS)2AlH2] [Li(TMEDA)2], 5

TMEDA (0.16 mL, 1.0 mmol) was added dropwise to a Schlenk flask containing a hexane (3 mL) solution of(HMDS)2Al(μ-H)2Li(OEt2)2, 2 (0.26 g, 0.5 mmol) which instantly forms a white precipitate. The reaction was stirred for 1.5 h, then the volatiles were removed giving the product as a white solid. (yield 0.50 g, 0.85 mmol, 85 %). Addition of toluene (3 mL) and cooling to -15 oC, produced colourless crystals suitable for single crystal X-ray analysis.

Synthesis of [(HMDS)2AlH2] [Li(Me6-TREN)], 6

Me6-tren (0.13 mL, 0.5 mmol) was added dropwise to a Schlenk flask containing a hexane (3 mL) solution of (HMDS)2Al(μ-H)2Li(OEt2)2, 2 (0.26 g, 0.5 mmol). The reaction was stirred for 1 h, which gave a white precipitate. Removing the volatiles under vacuum gives the product as a white solid (yield 0.26 g, 0.44 mmol, 89 %). Toluene (5 mL) was added and the Schlenk flask put in the freezer at -26oC, which produced colourless crystals suitable for X-ray.

Synthesis of (HMDS)2AlH(μ-H)Na(THF)3, 7

HMDS(H) (0.84 mL, 4 mmol) in THF (2 mL) was added dropwise to a cooled Schlenk flask containing a THF (2 mL) suspension of NaAlH4 (0.108 g, 2 mmol) at 0 oC. The resulting suspension was heated to 40 oC for three hours, then stirred at room temperature overnight. Filtering the suspension via a celite cannula generated a colourless solution. THF was removed under vacuum and the residues dissolved in hexane (5 mL). Cooling to –30 oC generated a crop of colourless crystals (yield 0.44 g, 0.75 mmol, 38 %).

Synthesis of (HMDS)2Al(μ-OCH2Ph)2Li(THF)2, 8

To a hexane (3 mL) solution of 1 (0.28 g; 0.5 mmol) was added 2 equivalents of benzaldehyde (0.10 mL; 1 mmol). The resulting clear, colourless solution was stirred at room temperature for 1.5 h then placed in the freezer at -30 oC. Colourless crystals of the product were isolated by cannula filtration. (Yield 0.15 g; 0.21 mmol; 42%)

Synthesis of [(HMDS)AlH(μH)[C3H4N3]Li(THF)], 9

To hexane (3 mL) was added LiAlH4 (0.5 mL, 1 mmol, 2M in THF), followed by HMDS(H) (0.84 mL, 4 mmol) and 1-methyl-1,2,4-triazole (0.08 mL, 1 mmol). The colourless solution was stirred for 15 minutes and then cooled to – 30 oC. Colourless crystals of the product were isolated by cannula filtration. (Yield 0.186 g; 0.53 mmol, 53 %)

DOSY NMR Spectroscopy

Diffusion-Ordered Spectroscopy (DOSY) NMR experiments were performed following the external calibration method introduced by Stalke. As such, 30mM concentration solutions of the lithium aluminate (0.015 mmol) in either C6D6 or d8-THF (0.5 mL) and either tetramethylsilane (0.015 mmol) or 1,2,3,4-tetraphenylnaphthalene (0.015 mmol) as internal standards.

Hydroboration Catalysis

Hydroboration catalysis was performed using the following general producer: The lithium aluminate catalyst 1,2, 3, 4, 5, 6, 7, 8 or LiAlH4 was added in the desired amount (0.005 mmol, i.e. 1 mol%, or 0.050 mmol, i.e. 10 mol%), and added to 0.5 mL of a C6D6or d8-THF solution containing 0.5 mmol of the carbonyl precursor and of pinacolborane (73 µL, 0.5 mmol), as well as 10 mol% of internal standard; hexamethylcyclotrisiloxane. The mixture was transferred to a sealed Young’s tap NMR tube and the reaction was regularly monitored by 1H and 11B NMR until the formation of products was completed. The reactions were performed at room temperature, except for substrates mesitaldehyde and 2,4,6-trimethyl acetophenone which were heated to 70 oC. The yields reported are based on 1H NMR relative to the internal standard. In all cases, the bulk of the NMR solution can be attributed to either the boronate esters or starting material.