Table 1.

Evaluation of monophosphite ligands L1–L4 in Rh-catalysed hydroformylation of styrene ^a.

Entry	Ligand (L)	P (bar)	T (°C)	Conversion (%)	Regio. (iso/n ratio)
1	-	10	80	96	50/50
2	L3-(S)-BINOL-(−)-menthol	10	80	99	61/39
3	L4-(R)-BINOL-(+)-menthol	10	80	99	59/41
4	L4-(R)-BINOL-(+)-menthol	20	80	99	65/35
5	L4-(R)-BINOL-(+)-menthol	25	80	99	64/36
6	L4-(R)-BINOL-(+)-menthol	20	50	92	94/6
7	L4-(R)-BINOL-(+)-menthol	25	50	95	96/4
8	L1-(S)-BINOL-(+)-menthol	25	50	93	96/4
9	L2-(R)-BINOL-(−)-menthol	25	50	94	96/4

^a Reaction conditions: 2.32 mmol styrene; 0.006 mmol Rh(CO)₂(acac), 0.03 mmol phosphite ligand; styrene/Rh = 400, P/Rh = 5, t = 4 h; Chemoselectivity for aldehydes was ≥ 99% in all cases.