DFT calculated free energies^c (kcal mol⁻¹) for the transformation of the Rh–alkyne species B_X–R to the Rh–vinylidene species 10_X–Rvia Pathway II.

X	R	TS(B-C)X–R		CX–R	TS(C-D)X–R		DX–R	10X–R
CH2	t Bu	+8.8	9.0	−3.0	+37.7	37.9	+36.4	−12.1
O	t Bu	+6.5	10.2	+1.3	+38.5	42.2	+37.0	−8.9
CH2	Ar′	+0.2	12.8	−4.5	+29.8a	42.4a	—b	−15.7
O	Ar′	+2.8	13.8	−1.0	+31.6a	42.6a	—b	−10.9

^aEstimated free energies by freezing the key distances in TS(C-D)_X–Ar.

^bTransition state is not calculated.

^cDFT method = BP86-D3(BJ)-1,2-difluorobenzene/BS2//BP86/BS1. Computed energy barriers ( and ) are relative to B_X–R. All free energies are quoted relative to 8_X (X = CH₂ and O, R = ^tBu and Ar′).