Oxidative addition and reductive elimination reactions are central steps in many catalytic processes, and controlling the energetics of reaction intermediates is key to enabling efficient catalysis. A series of oxidative addition and reductive elimination reactions using ( R PNP)RhX complexes (R = tert-butyl, isopropyl, mesityl, phenyl; X = Cl, I) was studied to deduce the effect of the size of the phosphine substituents. Using ( R PNP)RhCl as the starting material, oxidative addition of MeI was observed to produce ( R PNP)Rh(Me)(I)Cl, which was followed by reductive elimination of MeCl to form ( R PNP)RhI. The thermodynamics and kinetics vary with the identity of the substituent R on phosphorus of the PNP ligand. The presence of large steric bulk (e.g., R = tert-butyl, mesityl) on the phosphine favors Rh(I) in comparison to the presence of two smaller substituents (e.g., R = isopropyl, phenyl). An Eyring plot for the oxidative addition of MeI to ( tBu PNP)RhCl in THF-d 8 is consistent with a polar two-step reaction pathway, and the formation of [( tBu PNP)Rh(Me)I]I is also consistent with this mechanism. DFT calculations show that the steric bulk affects the reaction energies of addition reactions which generate six-coordinate complexes by tens of kcal mol −1 . The ligand steric bulk is calculated to have a reduced effect (a few kcal mol −1 ) on S N 2 addition barriers, which only require access to one side of the square plane.

Cp*Fe[P(OCH 2 ) 3 CEt] 2 Ph (Cp* = η 5 -1,2,3,4,5-pentamethylcyclopentadienyl, P(OCH 2 ) 3 CEt = 2,6,7-trioxa-1phosphabicyclo[2,2,1]heptane) reacts with furan and 2-methylfuran under photolytic conditions to selectively activate the α-C−H bond to produce Cp*Fe[P(OCH 2 ) 3 CEt] 2 (2-furyl) and Cp*Fe[P-(OCH 2 ) 3 CEt] 2 [2-(5-methylfuryl)], respectively. Cp*Fe[P-(OCH 2 ) 3 CEt] 2 (2-furyl) reacts with internal alkynes (2-butyne, 3hexyne, 1-phenyl-1-propyne) under photolytic conditions to produce sandwich complexes of the type Cp*Fe[η 5 -C 5 R 4 (CHCHCHO)] (R = alkyl and/or aryl). Experimental data suggest a mechanism that involves phosphite dissociation and successive alkyne insertions into the Fe−furyl bond followed by furyl ring opening. Similarly, the methylfuryl analogue Cp*Fe[P(OCH 2 ) 3 CEt] 2 [2-(5-methylfuryl)] reacts with 2-butyne to produce Cp*Fe[η 5 -C 5 Me 4 (CH CHCOCH 3 )].