Table 1.

Optimization of conditions for cyclometalation of 2‐bromobiphenyl (2 a).

Entry	Reagent (1.1 equiv)	T [°C]	t [min]	Conv. [%][b]	Yield [%][b,c]
1	nBuLi [a]	−50	30	100	0
2	nBu2 Mg	rt	60	23	0
3	nBu2 SmMe⋅5LiCl	−30 to rt	30	100	31[d]
4	nBu2 SmCl⋅4 LiCl	−30 to rt	30	100	40[d]
5	nBu2 LaCl⋅4 LiCl	−50	60	100	61[e]
6	nBu2 LaCl⋅4 LiCl	−50 to rt	30	100	89[e]
7	nBu2 LaCl⋅4 LiCl	−50 to 0	30	100	90(79[f])
8	nBu2 LaCl⋅4 LiCl	−50 to 0	60	100	80

[a] 2.2 equiv was used. [b] Determined by GC analysis. [c] The observed byproducts were mostly biphenyl, 2‐butylbiphenyl, and 2‐iodobiphenyl. [d] 2‐Butylbiphenyl was mainly generated. [e] 2‐Butylbiphenyl was observed in minor amounts. [f] Yield of isolated, analytically pure product.