The 13 C{ 1 H} NMR spectra of 2-4 (Figure ) and the 29 Si NMR spectrum of 4 (Figure ) show evidence of second order effects due to strong virtual coupling between the 31 P nuclei ( 2 JPP'). Similar effects have been reported in the literature for analogous phosphorus-carbon ABX and AA'X systems. Despite the different appearances of the 13 C{ 1 H} NMR signals, the 2 JCP and 3 JCP coupling constants are similar across the series [ 2 JCP = 10.7 Hz (2), 10.3 Hz (3), 10.2 Hz (4); 3 JCP = 3.6 Hz (1) 3.7 Hz (2), 3.5 Hz ( )]. This indicates that the differences between 2-4 are likely caused by the changing magnitude of 2 JPP' across the series.