The reaction of [Cl2OMo(mu-OC2H5)(2)(mu-HOC2H5)MoOCl2] (1) with 5 equiv of PMe(3) provides a simple route to pure mer-MoOCl2(PMe(3))(3) (3), so that its crystal structure could be determined [C9H27Cl2MoOP3, monoclinic, P2(1)/c, a = 17.138(3) Angstrom, b = 12.808(3) Angstrom, c = 19.226(4) Angstrom, beta = 115.99(1)degrees, Z = 8]. The mechanism of the conversion of 1 to 3 is complex, but one of the intermediates, MoOCl3(PMe(3))2 (4), can be isolated and crystallized, if 1 is reacted only with 3 instead of 5 equiv of PMe(3). 4 further reacts with an excess of PMe(3) to yield 3, providing additional evidence for its intermediacy. The crystal structure of 4 could be determined [C6H18Cl3MoOP2, monoclinic, P2(1)/n, a = 6.468(1) Angstrom, b = 12.677(2) Angstrom, c = 17.791(2) Angstrom, beta = 92.64(1)degrees, Z = 4]. If 4 is not isolated directly after the reaction and its crystallization is attempted from the raw mixture, two different compounds are obtained and their crystal structures were determined : MoOCl3(OPMe(3))(PMe(3)) (5) [C6H18Cl3 MoO2P2, monoclinic, P2(1)/n, a = 6.783(3) Angstrom, b = 12.623(4) Angstrom, c = 18.298(8) Angstrom, beta = 98.58(3)degrees, Z = 4] and Mo4O4Cl4(mu(2)-OC2H5)(4)(PMe(3))(2)(mu(3)-O)(2) (6) [C14H38Cl4Mo4O10P2, monoclinic, P2(1)/c, a = 1117.6(2) Angstrom, b = 1161.6(2) Angstrom, c = 1277.1(3) Angstrom, beta = 109.84(1)degrees, Z = 2]. 4 reacts slowly with CH2Cl2 producing [Me(3)PH](+)[MoOCl4(PMe(3))](-) (7), which can also be found among the products of attempts to crystallize 4 from CH2Cl2/petroleum ether mixtures, while its treatment with an excess of HCl produces [Me(3)PH](+)(2)[MoOCl5](2-) (8). The mechanism of the stepwise fragmentation of 1 yielding 3-7 is discussed.