Table 5. Photo-catalysis of [2 + 2] styrene cycloaddition ^a .

Entry	Cat.	Reaction time (h)	Substrate	Product	Conv.; yield (%) (d. r.) e
1	Pd-B-1	3			100; 88 (4 : 1) b
		4			27; 14 (4 : 1) d
2	Pd-N-1	4			100; 97 (4 : 1) c
		4			79; 73 (4 : 1) d
3	Pd-B-4	4			0; 0 b
		4			0; 0 c
4	fac-Ir(ppy)3	4			100; 77 (4 : 1) c
		4			76; 62 (4 : 1) d
5	—	4			0; 0 b
6	Pd-B-1	8.5			90; 74(>10 : 1) b
7	Pd-N-1	24			100; 82 (7 : 1) c
8	Pd-B-1	8.5			100; 94 (6 : 1) b
9	Pd-N-1	24			100; 97 (5 : 1) c
10	fac-Ir(ppy)3	24			100; 61 (6 : 1) c
11	Pd-B-1	8.5			100; 85 (7 : 1) b
12	Pd-N-1	16			>99; 80 (7 : 1) c
13	fac-Ir(ppy)3	16			>99; 79 (6 : 1) c

^aReaction condition: metal complex (1 mol%), substrate (0.01 mol dm^–3) in CH₃CN.

^bXenon lamp (λ_ex > 350 nm) as the light source.

^cblue LED (λ_em = 462 nm) as the light source.

^d23 W compact fluorescent lamp (CFL) as the light source.

^eProduct yield determined by ¹H NMR spectroscopy using 4,4′-dimethyl-2,2′-bipyridine as an internal standard.