The addition reaction of tetrakis(tetrahydrofuran)calcium or -strontium bis[bis(trimethylsilyl)phosphanide] with diphenylbutadiyne in toluene yields nearly quantitative amounts of slightly yellow tetrakis(tetrahydrofuran)calcium (1) and -strontium bis[2,5-diphenyl-3,4-bis(trimethylsilyl)phosphacyclopentadienide] (2). Due to the fact that the alkaline earth metal bis[bis(trimethylsilyl)amides] do not react with alkynes, colorless (tetrahydrofuran)calcium bis[2,5-bis(tert-butyl)-1-azacyclopentadienide] (3) was prepared by the transmetalation of N-trimethylstannyl-2,5-bis(tert-butyl)-1-azacyclopentadiene with distilled calcium. The metathesis reaction of 1 and 2 with SnCl2 gives yellow tin bis[2,5-diphenyl-3,4-bis(trimethylsilyl)phosphacyclopentadienide] (4). The phosphorus atoms of 1 and 2 are in a planar environment with long M-P distances, whereas in 4 the P atoms comprise a pyramidal coordination sphere. The tin-carbon distances are larger than observed in stannocenes which could be interpreted as a stannylene-like structure with sigma-bonded ligands. Crystallographic data for 1: monoclinic, C2/c, a = 2108.9(3) pm, b = 1296.2(2) pm, c = 2735.3(3) pm, beta = 93.37(1)degrees, Z = 4, wR2 = 0.1381 (all data, on F-2). Crystallographic data for 2: monoclinic, C2/c, a = 2104.7(1) pm, b = 1296.43(6)pm, c = 2717.8(1) pm, beta = 93.189(1)degrees, Z = 4, wR2 = 0.0954 (all data, on F-2). Crystallographic data for 4: triclinic, P (1) over bar, a = 1253.25(4) pm, b = 1312.58(4) pm, c = 1481.61(5) pm, alpha = 87.667(1)degrees, beta = 79.438(1)degrees, gamma = 72.684(1)degrees, Z = 2, wR2 = 0.0692 (all data, on F-2).