Nickelocene Reactions

Why is [NiBr2(PPh)3] tetrahedral and not square planar? (field stabilisation energy?) other than x-ray, how could you find out the geometry?

If we reacted nickelocene with dimethylacetylene dicarboxylate (DMAD) to form unknown A (Diels-Alder?), what would the electron count of A be? What would be a possible intermediate, considering hapticities and electron counts (in metallocenes)? Why wouldn't ferrocene react with DMAD the same way?

Propose a synthesis of 2,3-bis(methoxycarbonyl)norbornadiene.