▁rest ▁of ▁the ▁lig and ▁sphere ▁of ▁M . ▁ ▁When ▁the ▁complex ▁contains ▁two ▁or ▁four ▁identical ▁lig ands , ▁nearly ▁equal ▁M - N ▁distances ▁are ▁observed , ▁whereas , ▁when ▁different ▁or ▁odd - number ed ▁identical ▁lig ands ▁are ▁in ▁the ▁complex , ▁the ▁M - N ▁distances ▁are ▁all ▁of ▁significantly ▁different ▁length . ▁ ▁Syn thesis ▁ ▁Ph os phon im ines ▁with ▁the ▁formula ▁R 3 P = NS i Me 3 ▁are ▁particularly ▁useful . ▁They ▁are ▁prepared ▁by ▁the ▁Sta ud inger ▁reaction ▁of ▁t ert i ary ▁ph osph ines ▁with ▁trim eth yl s ily l ▁az ide : ▁R 3 P ▁ ▁+ ▁ ▁N 3 Si Me 3 ▁▁ ▁→ ▁▁ ▁R 3 P = NS i Me 3 ▁ ▁+ ▁ ▁N 2 ▁R 3 P = NS i Me 3 ▁under go es ▁alco hol ysis ▁to ▁give ▁the ▁parent ▁im ine : ▁R 3 P = NS i Me 3 ▁ ▁+ ▁ ▁Me OH ▁→ ▁▁ ▁R 3 P = N H ▁ ▁+ ▁ ▁Me OS i Me 3 ▁Am mon ia ▁can ▁be ▁used ▁in ▁place ▁of ▁alco hol . ▁ ▁Lith ium ▁ph osph in im ides ▁are ▁produced ▁by ▁de pro ton ation ▁of ▁the ▁parent ▁im ine : ▁R 3 P = N H ▁ ▁+ ▁ ▁R Li ▁→ ▁▁ ▁R 3 P = N Li ▁ ▁+ ▁ ▁R H ▁The ▁l ith io ▁derivatives , ▁which ▁exist ▁as