The reactivity of secondary phosphine oxides containing bulky organic fragments in hydrophosphinylation reactions has been investigated using several rhodium based catalysts. Upon heating in a focused microwave reactor, HP (O)(2-C6H4Me) 2 adds to prototypical terminal alkynes affording a complex mixture containing 1, 2 and 1, 1-addition products. Addition of a second ortho-substituent (HP (O) Mes2) completely suppresses the ...