The synthetic and structural organometallic chemistry of manganese(ii) is atypical of organotransition metal chemistry due to the observation of essentially ionic CÀMn II bonds, a property more commonly observed in organometallic compounds of the alkali and alkaline-earth metals. [1] Hence Mn II forms no isolable complexes with neutral p-acidic ligands such as carbon monoxide, olefins, or arenes, but does form an extensive series of cyclopentadienide (Cp À ) complexes such as manganocene, [Cp 2 Mn]. [2] Despite the ubiquitous nature of the cyclopentadienide ligand in organomanganese(ii) chemistry no examples of p coordination to an Mn II center by other anionic ligands of the "-enide" family are known: attempts at preparing "open manganocenes" that contain a bis-(h 5pentadienide)Mn arrangement, have only resulted in the formation of the unusual associated salts of general forumla [{(h 5 -pentadienide) 2 Mn I } 2 {m-Mn II }]. [3] Thus, we have sought to explore the capacity of the Mn II ion for forming stable complexes with other p-bonded ligands of the -enide family.
Since p coordination of the sterically hindered allyl (or propenide) ligand [1,3-(Me 3 Si) 2 C 3 H 3 ] À to a range of s-block metal cations has been observed, this ligand seemed the ideal candidate for use in the chemistry of the Mn II ion. [4] Furthermore, the stability and crystalline properties of the [(h-Cp) 3 M] À ions (M = Mn, Sn, Pb) suggested to us that the targeted synthesis of a tris(allyl)manganate anion would be prudent. [5] Thus we now report the synthesis and structure of [Mn{h 3 -(Me 3 Si) 2 C 3 H 3 }{h 1 -(Me 3 Si) 2 C 3 H 3 } 2 ][Li(thf) 4 ] ([1] [Li(thf) 4 ]), which a subsequent X-ray crystallographic analysis revealed to contain both s-and p-bonded [(Me 3 Si) 2 C 3 H 3 ] À allyl ligands. The anion 1 is the first structurally authenticated example of p-allyl coordination to a manganese(ii) center [Eq. ( 1)]. MnCl 2 þ 3 ½LifðMe 3 SiÞ 2 C 3 H 3 g thf À2 LiCl ! ½1½LiðthfÞ 4 ð 1Þ